15.2.13.1 SELECT ... INTO Statement

The SELECT ... INTO form of SELECT enables a query result to be stored in variables or written to a file:

• SELECT ... INTO var_list selects column values and stores them into variables.

• SELECT ... INTO OUTFILE writes the selected rows to a file. Column and line terminators can be specified to produce a specific output format.

• SELECT ... INTO DUMPFILE writes a single row to a file without any formatting.

A given SELECT statement can contain at most one INTO clause, although as shown by the SELECT syntax description (see Section 15.2.13, “SELECT Statement”), the INTO can appear in different positions:

• Before FROM. Example:

  SELECT * INTO @myvar FROM t1;

• Before a trailing locking clause. Example:

  SELECT * FROM t1 INTO @myvar FOR UPDATE;

• At the end of the SELECT. Example:

  SELECT * FROM t1 FOR UPDATE INTO @myvar;

The INTO position at the end of the statement is supported as of MySQL 8.0.20, and is the preferred position. The position before a locking clause is deprecated as of MySQL 8.0.20; expect support for it to be removed in a future version of MySQL. In other words, INTO after FROM but not at the end of the SELECT produces a warning.

An INTO clause should not be used in a nested SELECT because such a SELECT must return its result to the outer context. There are also constraints on the use of INTO within UNION statements; see Section 15.2.18, “UNION Clause”.

For the INTO var_list variant:

• var_list names a list of one or more variables, each of which can be a user-defined variable, stored procedure or function parameter, or stored program local variable. (Within a prepared SELECT ... INTO var_list statement, only user-defined variables are permitted; see Section 15.6.4.2, “Local Variable Scope and Resolution”.)

• The selected values are assigned to the variables. The number of variables must match the number of columns. The query should return a single row. If the query returns no rows, a warning with error code 1329 occurs (No data), and the variable values remain unchanged. If the query returns multiple rows, error 1172 occurs (Result consisted of more than one row). If it is possible that the statement may retrieve multiple rows, you can use LIMIT 1 to limit the result set to a single row.

  SELECT id, data INTO @x, @y FROM test.t1 LIMIT 1;

INTO var_list can also be used with a TABLE statement, subject to these restrictions:

• The number of variables must match the number of columns in the table.

• If the table contains more than one row, you must use LIMIT 1 to limit the result set to a single row. LIMIT 1 must precede the INTO keyword.

An example of such a statement is shown here:

TABLE employees ORDER BY lname DESC LIMIT 1
    INTO @id, @fname, @lname, @hired, @separated, @job_code, @store_id;

You can also select values from a VALUES statement that generates a single row into a set of user variables. In this case, you must employ a table alias, and you must assign each value from the value list to a variable. Each of the two statements shown here is equivalent to SET @x=2, @y=4, @z=8:

SELECT * FROM (VALUES ROW(2,4,8)) AS t INTO @x,@y,@z;

SELECT * FROM (VALUES ROW(2,4,8)) AS t(a,b,c) INTO @x,@y,@z;

User variable names are not case-sensitive. See Section 11.4, “User-Defined Variables”.

The SELECT ... INTO OUTFILE 'file_name' form of SELECT writes the selected rows to a file. The file is created on the server host, so you must have the FILE privilege to use this syntax. file_name cannot be an existing file, which among other things prevents files such as /etc/passwd and database tables from being modified. The character_set_filesystem system variable controls the interpretation of the file name.

The SELECT ... INTO OUTFILE statement is intended to enable dumping a table to a text file on the server host. To create the resulting file on some other host, SELECT ... INTO OUTFILE normally is unsuitable because there is no way to write a path to the file relative to the server host file system, unless the location of the file on the remote host can be accessed using a network-mapped path on the server host file system.

Alternatively, if the MySQL client software is installed on the remote host, you can use a client command such as mysql -e "SELECT ..." > file_name to generate the file on that host.

SELECT ... INTO OUTFILE is the complement of LOAD DATA. Column values are written converted to the character set specified in the CHARACTER SET clause. If no such clause is present, values are dumped using the binary character set. In effect, there is no character set conversion. If a result set contains columns in several character sets, so is the output data file, and it may not be possible to reload the file correctly.

The syntax for the export_options part of the statement consists of the same FIELDS and LINES clauses that are used with the LOAD DATA statement. For information about the FIELDS and LINES clauses, including their default values and permissible values, see Section 15.2.9, “LOAD DATA Statement”.

FIELDS ESCAPED BY controls how to write special characters. If the FIELDS ESCAPED BY character is not empty, it is used when necessary to avoid ambiguity as a prefix that precedes following characters on output:

• The FIELDS ESCAPED BY character

• The FIELDS [OPTIONALLY] ENCLOSED BY character

• The first character of the FIELDS TERMINATED BY and LINES TERMINATED BY values

• ASCII NUL (the zero-valued byte; what is actually written following the escape character is ASCII 0, not a zero-valued byte)

The FIELDS TERMINATED BY, ENCLOSED BY, ESCAPED BY, or LINES TERMINATED BY characters must be escaped so that you can read the file back in reliably. ASCII NUL is escaped to make it easier to view with some pagers.

The resulting file need not conform to SQL syntax, so nothing else need be escaped.

If the FIELDS ESCAPED BY character is empty, no characters are escaped and NULL is output as NULL, not \N. It is probably not a good idea to specify an empty escape character, particularly if field values in your data contain any of the characters in the list just given.

INTO OUTFILE can also be used with a TABLE statement when you want to dump all columns of a table into a text file. In this case, the ordering and number of rows can be controlled using ORDER BY and LIMIT; these clauses must precede INTO OUTFILE. TABLE ... INTO OUTFILE supports the same export_options as does SELECT ... INTO OUTFILE, and it is subject to the same restrictions on writing to the file system. An example of such a statement is shown here:

TABLE employees ORDER BY lname LIMIT 1000
    INTO OUTFILE '/tmp/employee_data_1.txt'
    FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"', ESCAPED BY '\'
    LINES TERMINATED BY '\n';

You can also use SELECT ... INTO OUTFILE with a VALUES statement to write values directly into a file. An example is shown here:

SELECT * FROM (VALUES ROW(1,2,3),ROW(4,5,6),ROW(7,8,9)) AS t
    INTO OUTFILE '/tmp/select-values.txt';

You must use a table alias; column aliases are also supported, and can optionally be used to write values only from desired columns. You can also use any or all of the export options supported by SELECT ... INTO OUTFILE to format the output to the file.

Here is an example that produces a file in the comma-separated values (CSV) format used by many programs:

SELECT a,b,a+b INTO OUTFILE '/tmp/result.txt'
  FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
  LINES TERMINATED BY '\n'
  FROM test_table;

If you use INTO DUMPFILE instead of INTO OUTFILE, MySQL writes only one row into the file, without any column or line termination and without performing any escape processing. This is useful for selecting a BLOB value and storing it in a file.

TABLE also supports INTO DUMPFILE. If the table contains more than one row, you must also use LIMIT 1 to limit the output to a single row. INTO DUMPFILE can also be used with SELECT * FROM (VALUES ROW()[, ...]) AS table_alias [LIMIT 1]. See Section 15.2.19, “VALUES Statement”.

Note

Any file created by INTO OUTFILE or INTO DUMPFILE is owned by the operating system user under whose account mysqld runs. (You should never run mysqld as root for this and other reasons.) As of MySQL 8.0.17, the umask for file creation is 0640; you must have sufficient access privileges to manipulate the file contents. Prior to MySQL 8.0.17, the umask is 0666 and the file is writable by all users on the server host.

If the secure_file_priv system variable is set to a nonempty directory name, the file to be written must be located in that directory.

In the context of SELECT ... INTO statements that occur as part of events executed by the Event Scheduler, diagnostics messages (not only errors, but also warnings) are written to the error log, and, on Windows, to the application event log. For additional information, see Section 27.4.5, “Event Scheduler Status”.

As of MySQL 8.0.22, support is provided for periodic synchronization of output files written to by SELECT INTO OUTFILE and SELECT INTO DUMPFILE, enabled by setting the select_into_disk_sync server system variable introduced in that version. Output buffer size and optional delay can be set using, respectively, select_into_buffer_size and select_into_disk_sync_delay. For more information, see the descriptions of these system variables.