Cross Joins

Every Left Pairs with Every Right

Every left row pairs with every right row.

highlighted = computed this step

Every row pairs

Each left row pairs with each right row.

every left with every right\text{every left with every right}

Read pair grid

The pair grid has 6 pairs.

pairs=6\text{pairs}=6

CROSS JOIN examples are tiny finite-table transforms; SQL dialect completeness, type coercion, optimizer behavior, execution cost, indexing, and database-product claims are out of scope.

Every left row pairs with every right row: left tablecolorredblue Every left row pairs with every right row: right tablesizeSML pair gridleftSourcerightSourceleftValuesrightValuesoutput00[red][S][red, S]01[red][M][red, M]02[red][L][red, L]10[blue][S][blue, S]11[blue][M][blue, M]12[blue][L][blue, L] CROSS JOIN output rowsleft.colorright.sizeredSredMredLblueSblueMblueL CROSS JOIN factsfactvalueleftRowCount2rightRowCount3pairCount6outputRowCount6outputColumnCount2rowOrderleft_source_then_right_sourceemptySideProductno

Pairs become output

Each pair becomes one output row.

one pair one row\text{one pair one row}

Summary

CROSS JOIN output is driven by pair count.

pair count drives output\text{pair count drives output}