3.0.0 • Public • Published


sql-client is a Node.js library that defines a simple and consistent abstraction for interacting with a relational database.


  • Simple and consistent API for multiple databases. (Currently PostgeSQL, MySQL and SQLite3 are supported, and support for additional database platforms shouldn't be difficult to implement.)

  • Prepared-statement-aware, with consistent ?-based bind-variable syntax. (Eliminating need for $n-style bindvar matching in PostgreSQL, although either style may be used.)

  • Easy-to-use transaction API with near seamless substitution between transactional and non-transactional database interactions.

  • Built-in (but optional) connection pooling, with:

    • pass-thru support to database-native pooling mechanism where available
      • configurable active and idle connection caps
      • configurable wait/block/grow/fail behavior when all connections are in use
      • optional keep-alive-while-idle, validation, automatic-retrieval and eviction policies
  • Batch (multi-statement) "SQL runner" available, with API and stand-alone command-line interfaces.

  • Small library with limited external dependencies.


Executing a Query

var sql_client = require('sql-client')
var client = new sql_client.PostgreSQLClient("postgres://uname:passwd@localhost/dbname")
client.execute( "SELECT 1 + ? AS x", [ 2 ], function (err, resultset) {
  console.log("The result is", resultset.rows[0].x) // yields `3`


var sql_client = require('sql-client')
var client = new sql_client.PostgreSQLClient("postgres://uname:passwd@localhost/dbname")

function create_table(client, callback) {
  sql = "CREATE TABLE employee ( name VARCHAR(64), salary INTEGER )"
  client.execute( sql, callback );

function insert_record(client, name, salary, callback) {
  sql = "INSERT INTO employee ( name, salary ) VALUES ( ?, ? )"
  client.execute( sql, [ name, salary ], callback )

function list_records(client, callback) {
  sql = "SELECT * FROM employee ORDER BY salary DESC"
  client.execute( sql, function(err, resultset) {
    if (err) {
    } else {
      for (i=0;i<resultset.rows.length;i++) {
        console.log(resultset.rows[i].name, resultset.rows[i].salary)
create_table( client, function() {
  insert_record( client, "Smith", 64000, function() {
    insert_record( client, "Hsu", 80000, function() {
      list_records( client, function() {

Connection Pooling

var sql_client = require('sql-client')

// configure and open the pool
var pool = new sql_client.PostgreSQLClientPool("postgres://uname:passwd@localhost/dbname")
var pool_options = {
  max_idle  : 3 // max number of idle connections to keep waiting in pool
  max_active: 5 // max number of active connections to allow at one time
pool.open( pool_options, function() {

  // automatically borrow and return across a single statement
  pool.execute( "SELECT 1 + ? AS x", [ 2 ], function (err, resultset) {
    console.log("The result is", resultset.rows[0].x) // yields `3`

    // or manually borrow and return for multiple statements
    pool.borrow( function(err, connection) {
      connection.execute("SELECT ...", function() {
        connection.execute("SELECT ...", function() {
          // ...and return when done
          pool.return(connection, function(){

            // close the pool to close all underlying connections

          }) // (end pool.return callback)
    }) // (end pool.borrow callback)

  }) // (end outer pool.execute callback)

}) // (end pool.open callback)


Via SQLClient Wrapper

var sql_client = require('sql-client')
var transaction = new Transaction(
  new sql_client.PostgreSQLClientPool("postgres://uname:passwd@localhost/dbname")
transaction.execute( "INSERT INTO employee ( name, salary )", [ "Jones", 40000 ], function (err) {
  if (err) {
    transaction.rollback(function() { callback(err); });
  } else {

Via SQLClientPool

var sql_client = require('sql-client')
var pool = new sql_client.PostgreSQLClientPool("postgres://uname:passwd@localhost/dbname")
pool.open( function() {

  // works just like a regular client, but with commit and rollback methods
  var transaction = pool.create_transaction();
  transaction.execute( "INSERT INTO employee ( name, salary )", [ "Jones", 40000 ], function (err) {
    if (err) {
      transaction.rollback(function() { callback(err); });
    } else {




sql-client is deployed as an npm module under the name sql-client. Hence you can install a pre-packaged version with the command:

npm install sql-client

and you can add it to your project as a dependency by adding a line like:

"sql-client": "latest"

to the dependencies or devDependencies section of your package.json file.

NOTE: You will also need to install the "native" client library for the database you are using. See below for details.

From Source

The source code and documentation for sql-client is available on GitHub at intellinote/sql-client.

You can clone the repository via:

git clone git@github.com:intellinote/sql-client

See the "Hacking" section below for tips on working with the source code.

Database-Specific Dependencies

In order to minimize external dependencies, although this library supports multiple database implementations it does not specify any of the "native" database-specific clients as a direct dependency. Instead, the specific database-client implementations that are exposed are determined at runtime, based on the third-party libraries that are available.

That means that in order to use sql-client with given database type you'll need to install one of the database-specific client libraries as a peer dependency. I.e., in addition to sql-client you'll want to add one (or more) of the following to the dependencies or devDependencies section of your package.json file:

  • For PostgreSQL, use npm install pg (or add "pg":"latest" in your package.json) to install node-postgres. Versions 7 and 8 of node-postgres are known to be supported. (Others are likely to be supported as well, but haven't necessarily been tested.)

  • For MySQL, use npm install mysql (or add "mysql":"latest" in your package.json) to install mysql. Version 2 of mySQL is known to be supported. (Other versions may also work, but haven't necessarily been tested.)

  • For SQLite, use npm install sqlite3 (or add "sqlite3":"latest" in your package.json) to install sqlite3. Versions 3 and 4 of sqlite3 are known to be supported. (Others may be supported as well, but haven't necessarily been tested.)

NOTE: sql-client works equally well with node-postgres v7 and v8, and with Node.js versions going back well before v14, but according to this issue you should use node-postgres v8 with Node.js version 14 or later. Specifically it seems that node-postgres v7 may hang indefinitely when attempting to connect to the database when running on Node v14. This issue is wholly independent of sql-client, we're just making a note of it because it can be hard to identify the source of the problem if you happen to encounter it.



SQLClient provides the core database-interaction functionality. It is roughly equivalent to a database "connection".

The abstract interface supports three methods:

SQLClient.connect(options, callback)

Open a connection to the database (based on the configuration provided to the database-specific constructor), or in some cases, borrow a connection from the underlying connection pool.


  • options - an optional map of database-specific options
  • callback - callback method with the signature (err)

The callback parameter is technically optional, but the client is not ready for use (i.e., the execute method cannot be called) until the callback (if provided) is invoked.

The callback method should accept a single parameter: an error (exception) object which will be populated if there was a problem connecting to the database. If the err parameter is undefined or null, the client is connected and ready to be used.

SQLClient.execute(sql, bindvars, callback)

Executes the given SQL statement, which may be a common CRUD (DQL/DML) statement like SELECT or INSERT, a DDL command such as CREATE TABLE or DROP FUNCTION or any arbitrary command accepted by the specific database instance (TRUNCATE, EXPLAIN, LOCK, etc.)


  • sql - the SQL statement to execute, as a string

  • bindvars - an optional array of bind-variable values; the nth element in the array will be bound to the nth bind variable slot (typically marked by ?) found in the SQL statement. Note that bind-variable substitution is NOT handled directly within sql-client but passed to the underlying database client library (which in turn submits the bind variables to the database engine itself using the native database network protocol).

  • callback - a callback method with a slightly database-dependent signature:

    • in PostgreSQL the signature is (err, result_set) where result_set is described here. Notably result_set.rows is an array of objects representing database records.
    • in SQLite3 the signature is (err, rows) where rows is an array of objects representing database records.
    • in MySQL the signature is (err, rows, fields) where rows is an array of objects representing database records and fields is a map of meta-data describing the columns in the result set.

SQLClient.disconnect(options, callback)

Close the connection to the database (or in some cases, return the connection to the pool). After disconnect is called the client can no longer be used.


  • options - an optional map of database-specific options
  • callback - callback method with the signature (err)


A pool of SQLClient instances that can be borrowed and returned.

SQLClientPool.open(options, callback)

Initialize the pool.


  • options - an optional map of configuration options, including:
    • min_idle - minimum number of idle connections in an "empty" pool (default: 0)
    • max_idle - maximum number of idle connections in a "full" pool (default: unset, no limit)
    • max_active - maximum number of connections active at one time (default: unset, no limit)
    • when_exhausted - what to do when max_active is reached (grow,block,fail) (default: grow - i.e., create a new connection anyway)
    • max_wait - when when_exhausted is block max time (in millis) to wait before failure, use < 0 for no maximum (default: unset, no limit)
    • wait_interval - when when_exhausted is BLOCK, amount of time (in millis) to wait before rechecking if connections are available (default: 50)
    • max_retries - number of times to attempt to create another new connection when a newly created connection is invalid; when null no retry attempts will be made; when < 0 an infinite number of retries will be attempted (default: unset, no limit)
    • retry_interval - when max_retries is > 0, amount of time (in millis) to wait before retrying (default: 50)
    • max_age - when a positive integer, connections that have been idle for max_age milliseconds will be considered invalid and eligable for eviction (default: unset, no limit)
    • eviction_run_interval - when a positive integer, the number of milliseconds between eviction runs; during an eviction run idle connections will be tested for validity and if invalid, evicted from the pool (default: unset, no eviction runs)
    • eviction_run_length - when a positive integer, the max number of connections to examine per eviction run (when not set, all idle connections will be examined during each eviction run) (default: unset, no limit)
    • unref_eviction_runner - unless false, unref will be called on the eviction run interval timer, which prevents the eviction-interval timer from keeping the node process alive when no other loops are active (default: true)
  • callback - callback method with the signature (err)


Terminate the pool, closing any idle connections.


  • callback - callback method with the signature (err)


Borrow a connection from the pool


  • callback - callback method with the signature (err, client)

SQLClientPool.return(client, callback)

Return a connection to the pool


  • client - the previously borrowed client
  • callback - callback method with the signature (err)

SQLClientPool.execute(sql, bindvars, callback)

Convenience method that is equivalent to borrowing a SQLClient instance, invoking execute on that client then returning the client to the pool.


Create a database transaction based on a connection borrowed from the pool.

A Transaction instance is essentially an extension of SQLClient with additional commit and rollback methods. Calling one of those methods will commit or rollback the database transaction and return the underlying connection to the database.

Note that you can also create a Transaction instance that wraps an instance of SQLClient directly (see below).


A Transaction wraps a SQLClient instance in a database transaction, adding commit and rollback methods that can be used to end the transaction.

A Transaction instance is obtained in one of two ways:

  1. By passing a SQLClient instance to the Transaction constructor, as in new Transaction(new SQLClient(...)).

  2. Via the create_transaction method of SQLClientPool (which see).

Once your work with the transaction is complete be sure to call Transaction.commit or Transaction.rollback to end the transaction. Both methods accept a callback method with the (err) signature.

Once a transaction has been closed via commit or rollback it can no longer be used.

Note that you may also BEGIN and subsequently COMMIT or ROLLBACK directly on the SQLClient instance to handle transactions "manually" (without using create_transaction or new Transaction(sql_client)).

Database-Specific Types

The sql-client module bundles support for several database platforms. Specifically:

  • PostgreSQLClient / PostgreSQLClientPool - a ConnectionFactory implementation that wraps node-postgres (known as pg on npm).

  • PostgreSQLClient2 / PostgreSQLClientPool2 - a ConnectionFactory implementation that wraps node-postgres but using node-postgres's built in pooling. (This client should be used with sql-client pool with max_idle = 0 to allow node-postgres to handle the pooling directly.)

  • MySQLClient / MySQLClientPool - a ConnectionFactory implementation that wraps mysql.

  • SQLite3Client / SQLite3ClientPool - a ConnectionFactory implementation that wraps sqlite3

These clients are generally implemented as thin wrappers around existing database-specific client modules.

Those database-specific modules are not declared as dependencies in this module's package.json file, and hence are not needed at runtime.

When sql-client is required, it will test to see if the requisite client libraries are available. The database-specific components of sql-client will only be loaded (and exported) if the underlying libraries they depend upon are available.

Hence, for example, the PostgreSQLClient and PostgreSQLClientPool classes depend on node-postgres.

To use sql-client with PostgreSQL, you'll need to install both node-postgres (npm install pg) and sql-client (npm install sql-client). In your package.json file, that would look something like this:

  "dependencies": {
    "pg": "latest",
    "sql-client": "latest"
  "...":"...and so on..."


When installed via npm, the sql-client module exposes a basic command line tool for executing arbitrary SQL (read from STDIN or files enumerated on the command line).

For example:

echo "SELECT 3+5 as FOO" | mysql-runner --db "mysql://sqlclient_test_u:password@localhost/sqlclient_test_db"

echo "SELECT 3+5 as FOO" | postgresql-runner --db "postgres://sqlclient_test_user:password@localhost/sqlclient_test_db"

echo "SELECT 3+5 as FOO" | sqlite3-runner --db ":memory:"

These files are available in the ./lib/bin, or (after make bin is run) in the ./bin directory, or (after npm install is run) in the ./node_modules/.bin directory.

Pass the command line parameter --help for more help.


The source-code distribution of this module contains a fairly extensive automated test suite, with ~75% coverage by line count.

These tests can be executed by running make test or npm test. A test-coverage report can be generated by running make coverage.

You should be able to simply clone the repository and successfully run the basic test suite (via just make test if you're using the Makefile, or npm install && npm test if you are not). There are however a few additional steps required to run the full test suite.

Automated functional tests are provided for each of the database-specific implementations of the core interface (PostgreSQL, MySQL, SQLite). However to execute these tests the following additional steps are required:

  1. You must install the corresponding "native" database client libraries as they are not listed as package dependencies by default. See the note above for details.

  2. In the case of MySQL and PostgreSQL you must set up a local "test" instance of the database for use during the tests. See the ./test/README.md file for instructions. (Since SQLite is an in-memory database this step is not required to test the sqlite3 implementation.)

If any database-specific library is missing when the test suite is run the corresponding tests will be skipped (but a prominent message will be printed to the console to warn you about this).

If the library is included but the external database instance cannot be reached the corresponding tests will fail (and a warning will be printed directing you to the test/README.md file).

For your convenience several targets have been added to the package.json file that allow you to run specify test collections:

  • npm test (or npm run-script test-all) will attempt to run all of the tests (including all database-specific "integration" tests)
  • npm run-script test-nodb will run the generic interface tests (those that do not depend on any specific database client library)
  • npm run-script test-pg will run the generic interface tests and the PostgreSQL-specific tests (but not SQLite or MySQL)
  • npm run-script test-sqlite will run the generic interface tests and the SQLite-specific tests (but not PostgeSQL or MySQL)
  • npm run-script test-mysql will run the generic interface tests and the MySQL-specific tests (but not PostgeSQL or SQLite)

Test Coverage

Run the Makefile target make coverage to generate a test coverage report. This will run the full automated test suite and generate a test coverage report (within ./docs/coverage) that contains an HTMLized view of the source code annotated with information about the functions, branches and lines that were exercised by the test run. As of this writing roughly 75% of the source code lines were touched by the complete automated test suite.


While not strictly required, you are strongly encouraged to take advantage of the Makefile when working on this module.

make is a very widely supported tool for dependency management and conditional compilation.

Obtaining Make

make is probably pre-installed on your Linux or Unix distribution (if not, you can use rpm, yum, apt-get, etc. to install it).

On Mac OSX, one simple way to add make to your system is to install the Apple Developer Tools from https://developer.apple.com/.

On Windows, you can install MinGW, GNUWin or Cygwin, among other sources.


With make installed, run:

make clean test

to download any missing dependencies, compile anything that needs to be compiled and run the unit test suite.


make docs

to generate various documentation artifacts, largely but not exclusively in the docs directory.

Using the Makefile

From this project's root directory (the directory containing this file), type make help to see a list of common targets, including:

  • make install - download and install all external dependencies.

  • make clean - remove all generated files.

  • make test - run the unit-test suite.

  • make bin - generate the executable scripts in ./bin.

  • make coverage - generate a test-coverage report (to the file docs/coverage.html).

  • make module - package the module for upload to npm.

  • make test-module-install - generates an npm module from this repository and validates that it can be installed using npm.


The sql-client library and related documentation are made available under an MIT License. For details, please see the file LICENSE.txt in the root directory of the repository.

How to contribute

Your contributions, bug reports and pull-requests are greatly appreciated.

We're happy to accept any help you can offer, but the following guidelines can help streamline the process for everyone.

  • You can report any bugs at github.com/intellinote/sql-client/issues.

    • We'll be able to address the issue more easily if you can provide an demonstration of the problem you are encountering. The best format for this demonstration is a failing unit test (like those found in ./test/), but your report is welcome with or without that.
  • Our preferred channel for contributions or changes to the source code and documentation is as a Git "patch" or "pull-request".

    • If you've never submitted a pull-request, here's one way to go about it:

      1. Fork or clone the repository.
      2. Create a local branch to contain your changes (git checkout -b my-new-branch).
      3. Make your changes and commit them to your local repository.
      4. Create a pull request as described here.
    • If you'd rather use a private (or just non-GitHub) repository, you might find these generic instructions on creating a "patch" with Git helpful.

  • If you are making changes to the code please ensure that the unit test suite still passes.

  • If you are making changes to the code to address a bug or introduce new features, we'd greatly appreciate it if you can provide one or more unit tests that demonstrate the bug or exercise the new feature.

  • This module follows the git-flow branching model. The master branch contains the latest production (released) code. The develop branch contains the work-in-progress. It would be best to submit any pull-requests against the develop branch.

Please Note: We'd rather have a contribution that doesn't follow these guidelines than no contribution at all. If you are confused or put-off by any of the above, your contribution is still welcome. Feel free to contribute or comment in whatever channel works for you.

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  • rodw
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