name) values(8, "Tom"),(8, "David"), (10, "Andy"); Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from t_index; +----+------+-------+ | id | age | name | +----+------+-
CONCAT_NULL_YIELDS_NULL QUOTED_IDENTIFIER NUMERIC_ROUNDABORT 会话选项设置为 OFF。 查询优化器查找视图索引列与查询中的元素之间的匹配项,例如: WHERE 子句中的搜索条件谓词 联接操作 聚合函数 GROUP BY 子句 表引用 估计的索引使用成本是查询优化器考虑使用的所有访问机制中的最低成本。 查询中引用(直接或通过展开...
SQL Server Combine two columns and aggregate into one valuePlease avoid images when forming questions...
CONCAT_WS Not Recognizable Concatenate a string to use after the AS statement Concatenate distinct values to variable concatenate numbers (not add them) CONCATENATE ROW_NUMBER WITH LEADING ZERO FOR MAXIMUM OF 15 CHARACTERS Concatenate two columns using a trigger Concatenated Stored Procedure parameter va...
||(CONCAT) 允許隱含交叉傳送至字串。 SQL 複製 -- A numeric is cast to STRING > SELECT 'This is a numeric: ' || 5.4E10; This is a numeric: 5.4E10 -- A date is cast to STRING > SELECT 'This is a date: ' || DATE'2021-11-30'; This is a date: 2021-11-30 date_add可以...
Extra中Using Index与Using Where,MySQL官方文档的解释如下:Using IndexThe column information is retrieved from the table using only information in the index tree without having to do an additional seek to read the actual row. This strategy can be used when the query uses only columns that are par...
good starting point. df_information_schema = vn.run_sql("SELECT * FROM INFORMATION_SCHEMA.COLUMNS...
<query_hint>::={ {HASH|ORDER}GROUP| {CONCAT|HASH|MERGE}UNION| {LOOP|MERGE|HASH}JOIN|DISABLE_OPTIMIZED_PLAN_FORCING|EXPANDVIEWS|FAST<integer_value>|FORCEORDER| {FORCE|DISABLE}EXTERNALPUSHDOWN| {FORCE|DISABLE}SCALEOUTEXECUTION|IGNORE_NONCLUSTERED_COLUMNSTORE_INDEX|KEEPPLAN|KEEPFIXEDPLAN|MAX_GRANT_PE...
{ MERGE | HASH | CONCAT } UNION Specifies that all UNION operations are run by merging, hashing, or concatenating UNION sets. If more than one UNION hint is specified, the Query Optimizer selects the least expensive strategy from those hints specified. Generally, a merge-based algo...
Errors when duplicate columns are referenced If your custom SQL query references duplicate columns, you may get errors when trying to use one of the columns in your analysis in Tableau. This will happen even if the query is valid. For example, consider the following query: SELECT * FROM auth...