STRPOS

Returns the position of the first occurrence of a substring, counting from 1, or 0 when it is not found.

Syntax

STRPOS( <string>, <substring> )

Argument	Description
`<string>`	The text to search.
`<substring>`	The text to find. Matched exactly, with case.

An integer: the character position of the first match, or 0 when there is none. 1 when <substring> is empty. NULL when any argument is NULL.

POSITION is the standard form with the arguments the other way round: POSITION(<substring> IN <string>).
The position counts characters, not bytes.
On large tables the engine runs it in the data store.

SELECT f.name, STRPOS(f.name, '.') AS dot
FROM tables.drive.file f
WHERE STRPOS(f.name, 'draft') > 0

name	dot
draft_plan.docx	11

With SUBSTRING, take the text before a character:

SELECT c.email, SUBSTRING(c.email, 1, STRPOS(c.email, '@') - 1) AS mailbox FROM Customer c

email	mailbox
ana.ruiz@example.com	ana.ruiz