UPDATE

Updates rows in the specified table.

Syntax 

UPDATE <table> [ [ AS ] <alias> ] SET <column1> = <expression1> [, <column2> = <expression2> ...] [ FROM from_item [, ...] ] WHERE <condition>

Parameters

Parameter Description
<table> The table name to update rows in.
<column> The name of the column to be updated.
<expression> An expression which computes a new value to populate the column. The expression can reference any column from the row being updated.
<from_item> A table expression allowing columns from other tables to appear in the WHERE condition and update expressions. This uses the same syntax as the FROM clause of a SELECT statement; for example, an alias for the table name can be specified. Do not repeat the target table as a from_item unless you intend a self-join (in which case it must appear with an alias in the from_item).
<condition> A Boolean expression. Only rows for which this expression returns true will be updated. Condition can have subqueries doing semi-join with other table(s).

Remarks

Updated rows are marked for deletion, but are not automatically cleaned up. You can monitor fragmentation in information_schema.tables to understand how many rows are marked for deletion out of total rows; fragmentation = (rows marked for deletion / total rows). Total row count in information_schema.tables excludes the number of rows marked for deletion. Query performance is not materially impacted by delete marks.

To mitigate fragmentation, use the VACUUM command to manually clean up deleted rows.

When a FROM clause is present, what essentially happens is that the target table is joined to the tables mentioned in the from_item list, and each output row of the join represents an update operation for the target table. When using FROM the join must produce at most one output row for each row to be modified. In other words, a target row shouldn’t join to more than one row from the other table(s).

Example with WHERE

The following example restocks product for which quantity is less than 10:

UPDATE product SET quantity = quantity + 10 WHERE quantity < 10

Table before:

name price quantity
wand 120 9
robe 80 1
broomstick 270 21
cauldron 20 16
quill 5 100

Table after:

name price quantity
wand 120 19
robe 80 11
broomstick 270 21
cauldron 20 16
quill 5 100

Example updating multiple columns

This example applies a discount and updates the quantity of a specific product.

UPDATE product SET price = 15, quantity = 100 WHERE name = 'cauldron'

Table before:

name price quantity
wand 120 9
broomstick 270 21
robe 80 1
cauldron 20 16
quill 5 100

Table after:

name price quantity
wand 120 9
broomstick 270 21
robe 80 1
cauldron 15 100
quill 5 100

Example updating with FROM

This example updates available stock count.

UPDATE product AS p SET quantity = p.quantity - s.amount FROM sales AS s WHERE p.name = s.name

Table product before:

name price quantity
wand 120 9
broomstick 270 21
robe 80 1
cauldron 20 16
quill 5 100

Table sales before:

name amount
wand 5
broomstick 3
quill 20

Table products after:

name price quantity
wand 120 4
broomstick 270 18
robe 80 1
cauldron 20 16
quill 5 80

Known limitations

Below are some known limitations of the UPDATE command.

  • UPDATE cannot be used on tables that have certain aggregating indexes An attempt to issue a UPDATE statement on a table with a join index or aggregating index outside of the below defined will fail - these table level aggregating indexes need to be dropped first. UPDATE can be used on tables that have aggregating indexes containing the following aggregating functions, starting in DB version 3.16.0: