When the condition is based on one column, I can use either IN, AND, or OR, but if the condition is based on two columns, how to write the query? For example, I need to set up the value of column 1 to NULL in the following rows: column 2 = ‘red’ AND column 3 =’ Monday’, column 2 = ‘yellow’ and column 3 = ‘Tuesday’. ‘red’ or ‘yellow’ is not unique in column 2, the same for ‘Monday’ and ‘Tuesday’. I have quite of few of rows need to be updated. How can I do this in one query?
column1 column2 column3 1 red Monday 2 red Tuesday 3 yellow Monday 4 yellow Tuesday 5 green Wednesday
The results look like this:
column1 column2 column3 NULL red Monday 2 red Tuesday 3 yellow Monday NULL yellow Tuesday 5 green Wednesday
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Answer
WHERE clauses boil down to a simple true/false value: true – the row matches, so do something. false – no match, don’t do anything.
If you have multiple independent conditions, then
WHERE (condition1) OR (condition2) OR ...
And each of those sub-conditions can be as arbitrarily complicated/simple as you need, including having their own in clauses:
WHERE (foo IN ('a','b','c')) OR (bar IN ('p','q', 'r')) OR (baz = 42)