If we want to remove unique constraint fromorderstable the following SQL can be used - ALTER TABLE orders DROP CONSTRAINT item_vendor_ukey; Add PRIMARY KEY constraint If we want to add a primary key constraint inorderstable the following SQL can be used. Only one primary key is allowed for...
* index as the determining columns. But as with check_functional_grouping(), * there's currently no way to represent dependency on a NOT NULL constraint, * so we consider only the pkey for now. */ static void remove_useless_groupby_columns(PlannerInfo *root) { Query *parse = root->par...
after the creation of the second index, can I remove the constraint index? If I can't remove the constraint index is it possible to change the order of an index? If not should I keep the two indexes? Thx for your help. postgresql index postgresql-performance index-tuning unique-constraint...
官网文档说到 应该对外键建索引,但考虑到索引不是一定要的,而且类型有多种,所以不自动对外键建锁引,所以我们应该手动建 Adding a unique constraint willautomatically create a unique B-tree indexon the column or group of columns listed in the constraint. A uniqueness restriction covering only some rows ...
we could treat any NOT-NULL columns appearing in a UNIQUE* index as the determining columns. But as with check_functional_grouping,* there's currently no way to represent dependency on a NOT NULL constraint,* so we consider only the pkey for now.*/staticvoidremove_useless_groupby_columns(Pl...
table_constraint ) INHERITS existing_table_to_inherit_from; 除了先前定义中列出的列之外,还继承现有表中的所有列。括号内的部分分为两部分:列定义和表约束。 PostgreSQL列和表定义 列定义遵循以下语法模式: column_namedata_type(optional_data_length_restriction)column_constraints ...
Postgresql 中的 Unique Index 和常见的用来加唯一约束的 unique constraint 的区别: http://www.postgresql.org/docs/9.2/static/indexes-unique.html 引用 PostgreSQLautomatically creates a unique index when a unique constraint or primary key is defined for a table. The index covers the columns that make...
* there's currently no way to represent dependency on a NOT NULL constraint, * so we consider only the pkey for now. */ staticvoid remove_useless_groupby_columns(PlannerInfo *root) { Query *parse = root->parse; Bitmapset **groupbyattnos; ...
remove_useless_joins清除无用的连接,比如以下的SQL语句: selectt1.dwbhfromt_grxx t1leftjoint_dwxx t2ont1.dwbh = t2.dwbh; 左连接,而且t_dwxx.dwbh唯一,这样的连接是不需要的连接,直接查询t_grxx即可. 从执行计划来看,PG只对t_grxx进行扫描:testdb=# explain verbose select t1.dwbh from t_grxx ...
keyIterator.remove(); } } if (CollectionUtils.isNotEmptyCollection(uniqueLockKeys)) { Set<String> obtainedLockNames = null; Connection connection = null; try { connection = DataSource.getConnection(); ObtainMultipleLocksResult result = LOCK_MANAGER.obtainLock( ...