LIKE Patterns

Underscore Single Character

Underscore covers exactly one character.

highlighted = computed this step

Underscore is one character

An underscore stands for exactly one character.

one character wildcard\text{one character wildcard}

Read underscore matches

The underscore pattern keeps 1 row.

TRUE rows=1\text{TRUE rows}=1

LIKE-pattern examples are tiny finite WHERE-style filters with a small SQL-like pattern subset; collations, escapes, dialect behavior, indexes, optimizer behavior, and product claims are out of scope.

Underscore is one character: base rowsidname1Ada2Al3Alan4Bea5Jo6NULL LIKE evaluationsourcevaluepatterntruthkept0Ada_oFALSEno1Al_oFALSEno2Alan_oFALSEno3Bea_oFALSEno4Jo_oTRUEyes5NULL_oUNKNOWNno LIKE output rowsidname5Jo LIKE factsfactvalueinputRowCount6outputRowCount1trueRows1falseRows4unknownRows1patternKindunderscorerowOrdersource_order

One slot only

Jo matches because the underscore covers J and the final letter is o.

one slot then o\text{one slot then o}

Summary

Underscore is not any length; it is one character.

exactly one\text{exactly one}