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Simple SQL escape and format for T-SQL (Example: Microsoft SQL Server). This is heavily influenced (and largely copied from) the great sqlstring library: https://www.npmjs.com/package/sqlstring


$ npm install tsqlstring


const SqlString = require('tsqlstring');

Escaping query values

Caution In order to avoid SQL Injection attacks, you should always escape any user provided data before using it inside a SQL query. You can do so using the SqlString.escape() method:

const userId = 'some user provided value';
const sql    = 'SELECT * FROM users WHERE id = ' + SqlString.escape(userId);
console.log(sql); // SELECT * FROM users WHERE id = 'some user provided value'

Alternatively, you can use ? characters as placeholders for values you would like to have escaped like this:

const userId = 1;
const sql    = SqlString.format('SELECT * FROM users WHERE id = ?', [userId]);
console.log(sql); // SELECT * FROM users WHERE id = 1

Multiple placeholders are mapped to values in the same order as passed. For example, in the following query foo equals a, bar equals b, baz equals c, and id will be userId:

const userId = 1;
const sql    = SqlString.format('UPDATE users SET foo = ?, bar = ?, baz = ? WHERE id = ?',
  ['a', 'b', 'c', userId]);
console.log(sql); // UPDATE users SET foo = 'a', bar = 'b', baz = 'c' WHERE id = 1

This looks similar to prepared statements in T-SQL, however it really just uses the same SqlString.escape() method internally.

Caution This also differs from prepared statements in that all ? are replaced, even those contained in comments and strings.

Different value types are escaped differently, here is how:

  • Numbers are left untouched
  • Booleans are converted to true / false
  • Date objects are converted to 'YYYY-mm-dd HH:ii:ss' strings
  • Buffers are converted to hex strings, e.g. X'0fa5'
  • Strings are safely escaped
  • Arrays are turned into list, e.g. ['a', 'b'] turns into 'a', 'b'
  • Nested arrays are turned into grouped lists (for bulk inserts), e.g. [['a', 'b'], ['c', 'd']] turns into ('a', 'b'), ('c', 'd')
  • Objects that have a toSqlString method will have .toSqlString() called and the returned value is used as the raw SQL.
  • Objects are turned into key = 'val' pairs for each enumerable property on the object. If the property's value is a function, it is skipped; if the property's value is an object, toString() is called on it and the returned value is used.
  • undefined / null are converted to NULL
  • NaN / Infinity are left as-is. T-SQL does not support these, and trying to insert them as values will trigger SQL Server errors until they implement support.

You may have noticed that this escaping allows you to do neat things like this:

const post  = {id: 1, title: 'Hello MySQL'};
const sql = SqlString.format('INSERT INTO posts SET ?', post);
console.log(sql); // INSERT INTO posts SET `id` = 1, `title` = 'Hello MySQL'

And the toSqlString method allows you to form complex queries with functions:

const GETDATE = { toSqlString: function() { return 'GETDATE()'; } };
const sql = SqlString.format('UPDATE posts SET modified = ? WHERE id = ?', [GETDATE, 42]);
console.log(sql); // UPDATE posts SET modified = GETDATE() WHERE id = 42

To generate objects with a toSqlString method, the SqlString.raw() method can be used. This creates an object that will be left un-touched when using in a ? placeholder, useful for using functions as dynamic values:

Caution The string provided to SqlString.raw() will skip all escaping functions when used, so be careful when passing in un-validated input.

const GETDATE = SqlString.raw('GETDATE()');
const sql = SqlString.format('UPDATE posts SET modified = ? WHERE id = ?', [GETDATE, 42]);
console.log(sql); // UPDATE posts SET modified = GETDATE() WHERE id = 42

If you feel the need to escape queries by yourself, you can also use the escaping function directly:

const sql = 'SELECT * FROM posts WHERE title=' + SqlString.escape('Hello SQL Server');
console.log(sql); // SELECT * FROM posts WHERE title='Hello SQL Server'

Escaping query identifiers

If you can't trust an SQL identifier (database / table / column name) because it is provided by a user, you should escape it with SqlString.escapeId(identifier) like this:

const sorter = 'date';
const sql    = 'SELECT * FROM posts ORDER BY ' + SqlString.escapeId(sorter);
console.log(sql); // SELECT * FROM posts ORDER BY [date]

It also supports adding qualified identifiers. It will escape both parts.

const sorter = 'date';
const sql    = 'SELECT * FROM posts ORDER BY ' + SqlString.escapeId('posts.' + sorter);
console.log(sql); // SELECT * FROM posts ORDER BY [posts].[date]

If you do not want to treat . as qualified identifiers, you can set the second argument to true in order to keep the string as a literal identifier:

const sorter = 'date.2';
const sql    = 'SELECT * FROM posts ORDER BY ' + SqlString.escapeId(sorter, true);
console.log(sql); // SELECT * FROM posts ORDER BY [date.2]

Alternatively, you can use ?? characters as placeholders for identifiers you would like to have escaped like this:

const userId = 1;
const columns = ['username', 'email'];
const sql     = SqlString.format('SELECT ?? FROM ?? WHERE id = ?', [columns, 'users', userId]);
console.log(sql); // SELECT [username], [email] FROM [users] WHERE id = 1

Please note that this last character sequence is experimental and syntax might change

When you pass an Object to .escape() or .format(), .escapeId() is used to avoid SQL injection in object keys.

Formatting queries

You can use SqlString.format to prepare a query with multiple insertion points, utilizing the proper escaping for ids and values. A simple example of this follows:

const userId  = 1;
const inserts = ['users', 'id', userId];
const sql     = SqlString.format('SELECT * FROM ?? WHERE ?? = ?', inserts);
console.log(sql); // SELECT * FROM [users] WHERE [id] = 1

Following this you then have a valid, escaped query that you can then send to the database safely. This is useful if you are looking to prepare the query before actually sending it to the database. You also have the option (but are not required) to pass in stringifyObject and timeZone, allowing you provide a custom means of turning objects into strings, as well as a location-specific/timezone-aware Date.

This can be further combined with the SqlString.raw() helper to generate SQL that includes T-SQL functions as dynamic vales:

const userId = 1;
const data   = { email: 'foobar@example.com', modified: SqlString.raw('GETDATE()') };
const sql    = SqlString.format('UPDATE ?? SET ? WHERE `id` = ?', ['users', data, userId]);
console.log(sql); // UPDATE [users] SET [email] = 'foobar@example.com', [modified] = GETDATE() WHERE [id] = 1




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