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WHERE filters the table you start with. For example, let’s break down this query that finds all owners with cats named “daisy”
SELECT owner
FROM cats
WHERE name = 'daisy'
FROM cats is pulling from a database with tables of cats and people.
| owner | name |
|---|---|
| 1 | daisy |
| 1 | dragonsnap |
| 3 | buttercup |
| 4 | rose |
WHERE name = 'daisy'
| owner | name |
|---|---|
| 1 | daisy |
SELECT owner
| owner |
|---|
| 1 |
What you can put in a WHERE :
expr LIKE…`
Check if a string contains a substring!
WHERE name LIKE '%darcy%'
(% is a wildcard, like * in your shell)
exprIN (...)
Check if an expression is in a fist of values
WHERE name IN ('bella', 'simba')
=, !=, <, >=
these work the way you’d guess, except when NULL is involved.
WHERE revenue - costs >=0
expr IS NULL, expr- IS NOT NULL
more about NULL on pages 15-17
= NULL (crossed out)
IS NULL (circled)
AND, OR, NOT
You can AND together as many conditions as you want
tiny little illustration of a smiling stick figure with curly hair: If I’m using lots of ANDs, like to write them like this:
(....)
AND (....)
AND (....)
(put all the ORs in the parentheses)
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