Syntax
------

Single-table syntax:

UPDATE [LOW_PRIORITY] [IGNORE] table_reference 
 [PARTITION (partition_list)]
 [FOR PORTION OF period FROM expr1 TO expr2]
 SET col1={expr1|DEFAULT} [,col2={expr2|DEFAULT}] ...
 [WHERE where_condition]
 [ORDER BY ...]
 [LIMIT row_count]

Multiple-table syntax:

UPDATE [LOW_PRIORITY] [IGNORE] table_references
  SET col1={expr1|DEFAULT} [, col2={expr2|DEFAULT}] ...
  [WHERE where_condition]

Description
-----------

For the single-table syntax, the UPDATE statement updates columns of existing
rows in the named table with new values. The SET clause indicates which
columns to modify and the values they should be given. Each value can be given
as an expression, or the keyword DEFAULT to set a column explicitly to its
default value. The WHERE clause, if given, specifies the conditions that
identify which rows to update. With no WHERE clause, all rows are updated. If
the ORDER BY clause is specified, the rows are updated in the order that is
specified. The LIMIT clause places a limit on the number of rows that can be
updated.

Until MariaDB 10.3.2, for the multiple-table syntax, UPDATE updates rows in
each table named in table_references that satisfy the conditions. In this
case, ORDER BY and LIMIT cannot be used. This restriction was lifted in
MariaDB 10.3.2 and both clauses can be used with multiple-table updates. An
UPDATE can also reference tables which are located in different databases; see
Identifier Qualifiers for the syntax.

where_condition is an expression that evaluates to true for each row to be
updated.

table_references and where_condition are as specified as described in SELECT.

For single-table updates, assignments are evaluated in left-to-right order,
while for multi-table updates, there is no guarantee of a particular order. If
the SIMULTANEOUS_ASSIGNMENT sql_mode (available from MariaDB 10.3.5) is set,
UPDATE statements evaluate all assignments simultaneously.

You need the UPDATE privilege only for columns referenced in an UPDATE that
are actually updated. You need only the SELECT privilege for any columns that
are read but not modified. See GRANT.

The UPDATE statement supports the following modifiers:

* If you use the LOW_PRIORITY keyword, execution of
 the UPDATE is delayed until no other clients are reading from
 the table. This affects only storage engines that use only table-level
 locking (MyISAM, MEMORY, MERGE). See HIGH_PRIORITY and LOW_PRIORITY clauses
for details.
* If you use the IGNORE keyword, the update statement does 
 not abort even if errors occur during the update. Rows for which
 duplicate-key conflicts occur are not updated. Rows for which columns are
 updated to values that would cause data conversion errors are updated to the
 closest valid values instead.

PARTITION
---------

See Partition Pruning and Selection for details.

FOR PORTION OF
--------------

MariaDB starting with 10.4.3
----------------------------
See Application Time Periods - Updating by Portion.

UPDATE Statements With the Same Source and Target
-------------------------------------------------

MariaDB starting with 10.3.2
----------------------------
From MariaDB 10.3.2, UPDATE statements may have the same source and target.

For example, given the following table:

DROP TABLE t1;
CREATE TABLE t1 (c1 INT, c2 INT);
INSERT INTO t1 VALUES (10,10), (20,20);

Until MariaDB 10.3.1, the following UPDATE statement would not work:

UPDATE t1 SET c1=c1+1 WHERE c2=(SELECT MAX(c2) FROM t1);
ERROR 1093 (HY000): Table 't1' is specified twice, 
 both as a target for 'UPDATE' and as a separate source for data

From MariaDB 10.3.2, the statement executes successfully:

UPDATE t1 SET c1=c1+1 WHERE c2=(SELECT MAX(c2) FROM t1);

SELECT * FROM t1;
+------+------+
| c1   | c2   |
+------+------+
|   10 |   10 |
|   21 |   20 |
+------+------+

Example
-------

Single-table syntax:

UPDATE table_name SET column1 = value1, column2 = value2 WHERE id=100;

Multiple-table syntax:

UPDATE tab1, tab2 SET tab1.column1 = value1, tab1.column2 = value2 WHERE
tab1.id = tab2.id;

URL: https://mariadb.com/kb/en/update/