The outer join basically creates the same resulting set as the inner join, with the difference that at least one line is created in the resulting set for every selected line on the left-hand side, even if no line on the right-hand side fulfils the join_cond condition. The columns on ...
通过一次索引就能找到数据,一般用于主键或唯一索引作为条件的查询sql中,执行sql如下: explain select * from test2 where id=1; 结果: eq_ref 常用于主键或唯一索引扫描。执行sql如下: explain select * from test2 t1 inner join test2 t2 on t1.id=t2.id; 结果: 此时,有人可能感到不解,const和eq_ref都是...
查询SQL如下: SELECT COUNT(*) FROM pq_test; EXPLAIN查询语句 不使用并行查询的执行情况 通过EXPLAIN语句查看不使用并行查询的执行情况。 查询语句如下: 查询结果如下: *** 1. row *** Id: 1 Select_type: SIMPLE Table: pq_test Partitions: NULL Type: index Possible_keys: NULL Key: PRIMARY Key_len...
sql语句:select t.* From teacher t INNER JOIN course c INNER JOIN teachercarid te WHERE t.tid = c.cid AND t.tcid = te.tcid AND (c.cid = 2 or te.tcid = 3); 执行结果: SQL语句很简单,我们不关心这个,我们关心的是在它前面加explain: explainselect t.* From teacher t INNER JOIN course...
syntaxsql複製 EXPLAIN[WITH_RECOMMENDATIONS]SQL_statement[;] 注意 Azure Synapse Analytics 的無伺服器 SQL 集區不支援此語法。 引數 SQL_statement 將執行 EXPLAIN 的 SQL 陳述式。SQL_statement可以是以下任一個命令:SELECT、INSERT、UPDATE、DELETE、CREATE TABLE AS SELECT、CREATE REMOTE TABLE。
In the following example, the operator ├─TableReader_28(Build) first reads the table t1. For each row that matches, TiDB will probe the table t2: EXPLAIN SELECT /*+ INL_JOIN(t1, t2) */ * FROM t1 INNER JOIN t2 ON t1.id = t2.t1_id; ...
For example, a query that uses the common subexpression optimization requires temporary tables to be created and analyzed in order to return the EXPLAIN output. The query plan depends on the schema and statistics of the temporary tables. Therefore, the EXPLAIN command for this type of query ...
EXPLAIN ANALYZE cannot be used with FOR CONNECTION. Example output: mysql> EXPLAIN ANALYZE SELECT * FROM t1 JOIN t2 ON (t1.c1 = t2.c2)\G *** 1. row *** EXPLAIN: -> Inner hash join (t2.c2 = t1.c1) (cost=3.5 rows=5) (actual time=0.121..0.131 rows=1 loops=1) -> Table...
半连接操作。inner_tables展示未拉出的表。详见 “Optimizing Subqueries, Derived Tables, and View References with Semijoin Transformations”[17] 14 <temporary table> 表示创建了内部临时表而缓存中间结果 当某些表是const或system类型时,这些表中的列所涉及的表达式将由优化器尽早评估,并且不属于所显示语句的一...
MaxCompute provides four task types: map, reduce, join, and local work. The first letter in a task name indicates the type of the task. For example, M2Stg1 is a map task. The digit that follows the first letter indicates the task ID. This ID is unique among all tasks that correspon...