PolarDB：DML支援GLOBAL INDEX SCAN

使用指南

• 建立分區表和全域索引（GLOBAL INDEX）：

  CREATE TABLE gi_ora
  (
      a int,
      b int,
      c int GENERATED ALWAYS AS (b * 2),
      d int DEFAULT 0,
      e int,
      f text,
      g text
  ) PARTITION BY RANGE (a)
  (
      partition p0 values less than (50),
      partition p1 values less than (100),
      partition p2 values less than (200),
      partition p3 values less than (300),
      partition p4 values less than (400),
      partition p5 values less than (500),
      partition p6 values less than (600),
      partition p7 values less than (700),
      partition p8 values less than (800)
  );
  
  INSERT INTO gi_ora(a,b,d,e,f,g) SELECT i,i,i, (random()*1000)::int,(random()*30000000)::int::text,(random()*30000000)::int::text FROM generate_series(1,799) i ;
  
  CREATE INDEX ON gi_ora(b) global;
  ANALYZE gi_ora;

• 使用GLOBAL INDEX SCAN對指定資料進行刪除操作：

  EXPLAIN (costs off, verbose on)  DELETE FROM gi_ora WHERE b = 198;

  顯示結果如下：

                                   QUERY PLAN
  ----------------------------------------------------------------------------
   DELETE ON global_index_dml.gi_ora
     ->  GLOBAL INDEX SCAN USING gi_ora_global_idx ON global_index_dml.gi_ora
           Output: gi_ora.tableoid, gi_ora.ctid
           Index Cond: (gi_ora.b = 198)
  (4 rows)

• 使用GLOBAL INDEX SCAN對指定資料進行更新操作：

  EXPLAIN (costs off, verbose on)  UPDATE gi_ora SET a = a - 10 WHERE b = 198;

  顯示結果如下：

                                   QUERY PLAN
  ----------------------------------------------------------------------------
   UPDATE ON global_index_dml.gi_ora
     ->  GLOBAL INDEX SCAN USING gi_ora_global_idx ON global_index_dml.gi_ora
           Output: (gi_ora.a - 10), gi_ora.tableoid, gi_ora.ctid
           Index Cond: (gi_ora.b = 198)
  (4 rows)