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23 cze 2013 · I am trying to UPDATE values from a table, but I need to add some conditions. I found the function CASE, but I am not if it is the best method. Here is an example. My table is 'relation': userid1 |
19 mar 2017 · With MySQL, I took advantage of the fact that you can have multiple NULL values in a unique index, so by adding a "tie breaker"(?) field, ucode, I was able to hack together a solution:
16 kwi 2016 · However, given how the conditions are re-used in your UPDATE statement, you could also take a different approach altogether: represent the affected IDs and the new values as a derived table and use an update with a join:
An UPDATE statement can start with a WITH clause to define common table expressions accessible within the UPDATE. See Section 15.2.20, “WITH (Common Table Expressions)”. Single-table syntax: UPDATE [LOW_PRIORITY] [IGNORE] table_reference . SET assignment_list . [WHERE where_condition] [ORDER BY ...] [LIMIT row_count] value: {expr | DEFAULT}
26 sty 2024 · When a UNIQUE constraint violation occurs, MySQL raises an error. To handle these situations, developers may use conditional logic, such as the ‘on duplicate key update’ clause, or exception handling in application-level code to manage such errors graciously.
If you insert or update a value that causes a duplicate in the column1, MySQL rejects the change and issues an error. This UNIQUE constraint is a column constraint. And you can use it to enforce the unique rule for one column.
18 lut 2018 · It is possible to update rows based on some condition. It is also possible to update multiple tables in one statement in MySQL. Whether the latter is a good idea is debatable, though.
