mysql - merge two large tables with unique values -


i have large tables, main 1 (tablea) around 14 million records , second 1 want merge 20 million records (tableb). part first subset of second.

i tried making unique index using 2 or 3 fields combined identify records such mysql wouldn't it.

i made own field 'unique' concatenating 3 fields.

my question how import tableb tablea using unique records i.e. ones value in unique field in tableb not exist in unique field in tablea. since not make unique field actual unique index will/should try make each 1 pk , or ordinary index in respective tables?

any thoughts on how efficiently appreciated.

use sql union statement.

    "select * tablea join tableb"

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