See Section 11.2.2, “Identifier Qualifiers”, for examples of ambiguity that require the more explicit column reference forms. A table reference can be aliased using tbl_name AS alias_name or tbl_name alias_name. These statements are equivalent: SELECT t1.name, t2.salary FROM employee AS...
A correlated subquery is a query that depends on the outer query for its values. This query can be executed repeatedly, one time for each row that could be selected by the outer query. The first example shows queries that are semantically equivalent to illustrate the difference between using ...
A flashback query cannot span statements that affect the table structure or physical storage. Otherwise, an error is reported. Between the flashback point and the current point, if a statement (TRUNCATE, DDL, DCL, or VACUUM FULL) has been executed to modify the table structure or affect phys...
rather than sorting the entire result. If ordering is done by using an index, this is very fast. If a filesort must be done, all rows that match the query without the LIMIT clause are selected, and most or all of them are
Instructs the kernel not to reveal the actual values used in where clauses to the SQL Server database at the time of optimization. This is the default in all statements that are not join statements. The advantage of using this keyword is that the kernel can reuse the access plan for othe...
Instructs the kernel not to reveal the actual values used in where clauses to the SQL Server database at the time of optimization. This is the default in all statements that are not join statements. The advantage of using this keyword is that the kernel can reuse the access plan for othe...
A table reference can be aliased usingtbl_nameASalias_nameortbl_name alias_name. These statements are equivalent: SELECTt1.name,t2.salaryFROMemployeeASt1,infoASt2WHEREt1.name=t2.name;SELECTt1.name,t2.salaryFROMemployee t1,info t2WHEREt1.name=t2.name; ...
This topic describes the syntax of SELECT statements in MaxCompute. This topic also describes how to use SELECT statements to perform operations, such as nested queries, sorting, and queries by group. Before you execute SELECT statements, make sure that you are granted the Select permission on ...
After removing parentheses and grouping operations to the left, that join expression transforms into this expression: (t1LEFTJOINt2ONt1.a=t2.a)LEFTJOINt3ONt2.b=t3.bORt2.bISNULL Yet, the two expressions are not equivalent. To see this, suppose that the tables t1, t2, and t3 have the ...
It is recommended that the number of conditions be less than or equal to 100 to prevent high dynamic memory. If the WHERE IN candidate subset is too large, the memory usage of the generated plan increases. If the WHERE IN subsets constructed by concatenated SQL statements are different, the...