CASE Expressions

First TRUE Branch Wins

The first TRUE branch supplies the result.

highlighted = computed this step

First TRUE branch wins

When a row has a TRUE branch, CASE uses that branch result.

first TRUE wins\text{first TRUE wins}

Read TRUE branch rows

The CASE expression takes a TRUE branch for 2 rows.

TRUE branch rows=2\text{TRUE branch rows}=2

CASE-expression examples are tiny finite row transforms with SQL-style TRUE/FALSE/UNKNOWN logic; SQL dialect completeness, type coercion, optimizer behavior, indexing, and product claims are out of scope.

First TRUE branch wins: base rowsnamescorestatusAda90activeBea40activeCalNULLactiveDee70paused CASE branch evaluationsourcevaluesevaluationsresultresultSource0[Ada, 90, active][{branch:0, truth:TRUE, chosen:yes}, {branch:1, truth:TRUE, chosen:no}]highbranch 01[Bea, 40, active][{branch:0, truth:FALSE, chosen:no}, {branch:1, truth:FALSE, chosen:no}]lowELSE2[Cal, NULL, active][{branch:0, truth:UNKNOWN, chosen:no}, {branch:1, truth:UNKNOWN, chosen:no}]lowELSE3[Dee, 70, paused][{branch:0, truth:FALSE, chosen:no}, {branch:1, truth:TRUE, chosen:yes}]midbranch 1 CASE output rowsnamescorestatusbucketAda90activehighBea40activelowCalNULLactivelowDee70pausedmid CASE factsfactvalueinputRowCount4branchCount2outputRowCount4firstTrueRows2elseRows2nullElseRows0unknownSkipped2rowOrdersource_order

Do not keep looking

After the first TRUE branch is chosen, later branches do not replace it.

stop at first TRUE\text{stop at first TRUE}

Summary

CASE is an ordered choice, not a vote across all branches.

ordered choice\text{ordered choice}