Check Constraints

Required Cells

A NOT NULL rule catches a missing cell.

highlighted = computed this step

Required cells

A NOT NULL rule says this column must contain a real cell, not NULL.

status is required\text{status is required}

Find the missing cell

The compiler finds 1 violation, so 1 row fails.

violations=1\text{violations}=1

Check examples are tiny finite row-rule validations; SQL dialects, DDL timing, CHECK expression languages, enforcement strategy, performance, and product behavior are out of scope.

Required cells: tableidstatusqty1new22NULL43done5 row rulesnamekindcolumndetailstatus_requirednot_nullstatusnot NULL row pass/failrowstatusfailed rules0pass[]1fail[status_required]2pass[] violationsrowrulecolumnvaluereason1status_requiredstatusNULLNULL check factsfactvaluerowCount3ruleCount1passCount2failCount1violationCount1allRowsPassnonullMeansMissingyes

Read the failed row

The violations table points at the row, rule, column, value, and reason.

NULL is visible\text{NULL is visible}

Summary

NULL is treated as missing for this row-rule model.

NULL means missing here\text{NULL means missing here}