TheWITH query_name clause lets you assign a name to a subquery block. You can then reference the subquery block multiple places in the query by specifying the query name. Oracle optimizes the query by treating the query name as either an inline view or as a temporary table. (WITH语句只能...
We can also use the SQL-99 “WITH clause” instead of temporary tables. The Oracle SQL “WITH clause” will compute the aggregation once, give it a name, and allow us to reference it (maybe multiple times), later in the query. The SQL-99 “WITH clause” is very confusing at first b...
A join is a query that combines rows from two or more tables, views, or materialized views. Oracle Database performs a join whenever multiple tables appear in the FROM clause of the query. The select list of the query can select any columns from any of these tables. If any two of thes...
SQL macros and WITH clause are not known to be great friends: you cannot call a SQL macro in a WITH clause and if you want to define a table macro returning a query containing a WITH subquery(ies), then you won’t be able to use scalar parameters in this subquery. In theprevious po...
A table lock, also called a TM lock, is acquired by a transaction when a table is modified by an INSERT, UPDATE, DELETE, MERGE, SELECT with the FOR UPDATE clause, or LOCK TABLE statement. DML operations require table locks to reserve DML access to the table on behalf of a transaction ...
一、 拆分/拼接SQL 1. 拆分循环执行 例如有10000个值要in,就拆成10个20个语句循环执行,然后再处理结果。如果能拆得比较小,SQL能走上索引,其实还可以;如果拆出来都是大表走全表扫描,那就窒息了。 还遇到过有种极致的拆法:拆成一条条ID=xxx去执行,如果数据量大,通常性能不如小批量的in,还是需要测试出一个...
Introduction to Oracle FULL OUTER JOIN clause# Suppose you have two tables T1 and T2. The following illustrates the full outer join of the two tables: SELECTselect_listFROMT1FULLOUTERJOINT2ONjoin_condition;Code language:SQL (Structured Query Language)(sql) ...
Oracle LEFT JOIN with USING clause# Oracle allows you to use theUSINGclause to implicitly test for equality (=) when joining tables. Here’s the syntax of theLEFT JOINwith theUSINGclause: SELECTcolumn_listFROMXLEFTJOINYUSING(id);Code language:SQL (Structured Query Language)(sql) ...
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Deletes one or more lines of the SQL buffer ("*" indicates the current line). You can omit the space between DEL and n or *, but not between DEL and LAST. Enter DEL with no clauses to delete the current line of the buffer. The buffer has no command history list and does not re...