Oracle 列A=列A 相当于列不为空，条件无意义

SELECT COUNT(*) FROM table WHERE cola = cola

Plan Hash Value : 1132397616

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| Id | Operation | Name | Rows | Bytes | Cost | Time |

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| 0 | SELECT STATEMENT | | 1 | 3 | 53010 | 00:00:03 |

| 1 | SORT AGGREGATE | | 1 | 3 | | |

| 2 | PARTITION LIST ALL | | 5766973 | 17300919 | 53010 | 00:00:03 |

| * 3 | TABLE ACCESS FULL | table | 5766973 | 17300919 | 53010 | 00:00:03 |

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Predicate Information (identified by operation id):

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* 3 - filter("cola" IS NOT NULL)