question: private static boolean createConstraintOnPostgres ( ConnectionSource connectionSource , String constraintName , String constraintStatement ) throws SQLException { Preconditions . checkArgument ( isUnquotedSqlIdentifier ( constraintName ) , "invalid constraint name: %s" , constraintName ) ; if ( ! ( connectionSource . getDatabaseType ( ) instanceof PostgresDatabaseType ) ) { logger . warn ( "Not creating constraint {}: DB is not Postgres" , constraintName ) ; return false ; } String queryString = "SELECT count(*) FROM pg_constraint WHERE conname = '" + constraintName + "';" ; long constraintCount = connectionSource . getReadOnlyConnection ( ) . queryForLong ( queryString ) ; if ( constraintCount != 0 ) { assert constraintCount == 1 ; return false ; } logger . info ( "Creating constraint {}" , constraintName ) ; connectionSource . getReadWriteConnection ( ) . executeStatement ( constraintStatement , DatabaseConnection . DEFAULT_RESULT_FLAGS ) ; assert connectionSource . getReadOnlyConnection ( ) . queryForLong ( queryString ) == 1 ; return true ; }
target:  If using Postgres and constaintName doesn't exist, it executes constraintStatement to create it.