Mysql statement: Batch update different values of multiple records

 

The mysql update statement is simple. to update a field of a piece of data, write as follows:

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1	UPDATE mytable SET myfield = 'value' WHERE other_field = 'other_value';

If the same field is updated to the same value, mysql is also very simple. modify where:

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1	UPDATE mytable SET myfield = 'value' WHERE other_field in ('other_values');

Note that 'other _ values' is a comma (,)-separated string, for example, 1, 2, 3.

If multiple data entries are updated with different values, many may write as follows:

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1234	foreach ($display_order as $id => $ordinal) {    $sql = "UPDATE categories SET display_order = $ordinal WHERE id = $id";    mysql_query($sql);}

It is an update record that repeats one by one. Update a record once, which has poor performance and can easily cause blocking.

Can I update an SQL statement in batches? Mysql does not provide a direct method for batch update, but it can be implemented with tips.

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UPDATE mytable    SET myfield = CASE id        WHEN 1 THEN 'value'        WHEN 2 THEN 'value'        WHEN 3 THEN 'value'    ENDWHERE id IN (1,2,3)

Here we use the case when tip to implement batch update.
For example:

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UPDATE categories    SET display_order = CASE id        WHEN 1 THEN 3        WHEN 2 THEN 4        WHEN 3 THEN 5    ENDWHERE id IN (1,2,3)

This SQL statement indicates that the display_order field is updated. If id = 1, the value of display_order is 3. If id = 2, the value of display_order is 4, if id = 3, the value of display_order is 5.
The condition statements are written together.
The where part does not affect code execution, but it increases the SQL Execution efficiency. Make sure that the SQL statement only executes the number of rows to be modified. Here, only three rows of data are updated, and the where clause ensures that only three rows of data are executed.

If you want to update multiple values, you only need to slightly modify them:

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UPDATE categories    SET display_order = CASE id        WHEN 1 THEN 3        WHEN 2 THEN 4        WHEN 3 THEN 5    END,    title = CASE id        WHEN 1 THEN 'New Title 1'        WHEN 2 THEN 'New Title 2'        WHEN 3 THEN 'New Title 3'    ENDWHERE id IN (1,2,3)

At this point, a mysql statement has been completed to update multiple records.
But to use it in the business, you need to combine the server language. Here we take php as an example to construct this mysql statement:

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$display_order = array(    1 => 4,    2 => 1,    3 => 2,    4 => 3,    5 => 9,    6 => 5,    7 => 8,    8 => 9);$ids = implode(',', array_keys($display_order));$sql = "UPDATE categories SET display_order = CASE id ";foreach ($display_order as $id => $ordinal) {    $sql .= sprintf("WHEN %d THEN %d ", $id, $ordinal);}$sql .= "END WHERE id IN ($ids)";echo $sql;

In this example, eight records are updated. The code is easy to understand. Have you learned it?

 

Reference: http://www.ghugo.com/update-multiple-rows-with-different-values-and-a-single-sql-query/