SQL: fix + test handling columns argument in read_table
ENH: Use Float64HashTable for Float64Index backend
Merge pull request #6879 from cpcloud/float64-index-enh

ENH: Float64Index now uses Float64Hashtable as a backend
ENH/TST SQL: add multi-index support to to_sql
ENH/TST SQL: add multi-index support to read_table
Merge pull request #6735 from jorisvandenbossche/sql-multiindex

ENH: SQL multiindex support
SQL: add multi-index support to legacy mode (#6881)

and at once also index_label kwarg support
SQL: keep backwards compatibility for write_frame index handling
Merge pull request #6883 from jorisvandenbossche/sql-multiindex

SQL: add multi-index support to legacy mode
API: add is_beg_month/quarter/year, is_end_month/quarter/year accessors (#4565)