背景是在一台11gR2的机器上,开发反映一个批处理比以前慢了3倍.经过仔细查看该SQL的执行计划,发现由于SQL中使用了or,导致CBO走出了一个非常糟糕的CONCATENATION路径. no_expand提示的说明是 The NO_EXPAND hint prevents the cost-based optimizer from considering OR-expansion for queries having OR conditions or IN-lists in the WHER…
B. Cells Not Under Attack time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Vasya has the square chessboard of size n × n and m rooks. Initially the chessboard is empty. Vasya will consequen…