How to use explain in oracle

The EXPLAIN command in Oracle is used to analyze the execution plan of a SQL statement. The method of use is to add the EXPLAIN keyword before the SQL statement. EXPLAIN results contain information such as ID, operator type, row count estimate, cost estimate, output row count estimate, access predicates, and filter predicates, which can be used to optimize query performance, identify costly operators, and tables that may benefit from optimization techniques.

Usage of EXPLAIN in Oracle

The EXPLAIN command is used to analyze the execution plan of SQL statements to help developers understand Statement execution logic and optimization strategy.

How to use

When using the EXPLAIN command, just add the EXPLAIN keyword before the SQL statement. The syntax is as follows:

<code>EXPLAIN [FORMAT {ALL|BRIEF|EXTENDED}] [AS XML|JSON|MARKDOWN] <SQL语句></code>

Among them:

• The FORMAT option specifies the format of the EXPLAIN result.
• AS option specifies the output format of EXPLAIN results, which can be XML, JSON or MARKDOWN.

Explain the results

The output of the EXPLAIN command usually contains the following information:

• ID: The unique identifier of the operator.
• Operation: Operator type, such as table scan, index scan or join.
• Rows: An estimate of the number of rows processed by this operation.
• Cost: The estimated cost of this operation.
• Cardinality: Output row count estimate.
• Access Predicates: Predicates used to access data.
• Filter Predicates: Predicates for filtering output rows.

Usage Guide

• Use the EXPLAIN command to optimize query performance.
• Identifies costly operators in the query plan.
• Identify tables that may benefit from indexes or other optimization techniques.
• Avoid using expensive operators such as full table scans.
• Use the FORMAT option to customize the format of EXPLAIN results.
• Use the AS option to export EXPLAIN results in different formats for easier analysis and reporting.

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