Updating tables in sql from another table
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The prudent use of temporary tables can dramatically improve Oracle SQL performance.To illustrate the concept, consider the following example from the DBA world.
If the amount of data to be processed or utilized from your PL/SQL procedure is too large to fit comfortably in a PL/SQL table, use a GLOBAL TEMPORARY table rather than a normal table.This chapter explains how to create and use PL/SQL collection and record variables.These composite variables have internal components that you can treat as individual variables.Using the same key with a different value changes the value.Example 5-1 declares an associative array that is indexed by a string, populates it, and prints it.A nested table type or varray type that is created at schema level (with the CREATE TYPE Statement) is stored in the database, and you can manipulate it with SQL statements.
A collection has only one dimension, but you can model a multidimensional collection by creating a collection whose elements are also collections.For certain types of SQL operations, the creation of intermediate result tables can result in stunning performance improvements.We will discuss how you can use the global temporary tables (GTT) syntax to improve the speed of queries that perform complex summarization activities, and how to speed up two-stage queries that perform both summarization and comparison activities.A computed column is a virtual column that is not physically stored in the table, unless the column is marked PERSISTED.The column is computed from an expression that uses other columns in the same table.--Disk-Based CREATE TABLE Syntax CREATE TABLE [ database_name . For more information about File Tables, see File Tables (SQL Server).