AppendHead sets [1, 2, 3, 4] to [2, 3, 4, 1].

Filter filters the columns inplace.

Group the columns with the same type.

PrependTail sets [1, 2, 3, 4] to [4, 1, 2, 3].

partition p0 values in (v0, v1, v2), partition p1...

(col1, col2...) = (val11, val12...) or (col1, col2...) = (val21, val22...)...

(col1 = val11 and col2 = val12 and ...) or (col1 = val21 and col2 = val22 and ...) ...

(col1, col2...) in ((val11, val12...), (val21, val22...), ...).

partition p0 values less than (v0), partition p1...

RandomCompatibleColumnPair select 2 columns that have the compatible types.

Make a list of string into random groups, and filter the empty groups.

Str is a Fn which simply returns str.

SwapOutParameterizedColumns substitute random Columns with `?` for prepare statements.

a replacement to avoid initialization loop.

QueryState represent an intermediate state during a query generation.

ColumnTypeGroup stores column types -> Columns.