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POPSTypes of SQL Statements The tables in the following sections provide a functional summary of SQL statements and are divided into these categories: * Data Definition Language (DDL) Statements * Data Manipulation Language (DML) Statements * Transaction Control Statements * Session Control Statements * System Control Statements
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POPSOracle DBA - Comments Comments within sql statements do not affect the statement execution, but they may make your application easier for you to read and maintain. You may want to include a comment in a statement that describes the statement's purpose within your application.
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POPSOracle DBA - Pseudocolumns A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values
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POPSOracle DBA - Nulls If a column in a row has no value, then the column is said to be null, or to contain a null. Nulls can appear in columns of any datatype that are not restricted by NOT NULL or PRIMARY KEY integrity constraints. Use a null when the actual value is not known or when a value would not be meaningful.
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POPSOracle DBA - Migration Tools Migration tools are used to transfer the loads of data from one database to another or from one version of the database to other version of database.