SQL

SQL (Structured Query Language) is a standard language used to operate relational databases. It includes operations such as database creation, retrieving and modifying data, granting privileges to data.

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INNER JOIN and OUTER JOIN Explained

Overview of INNER JOIN and OUTER JOIN in Oracle, with examples, memory aids and a further drilldown of INNER JOIN and OUTER JOIN types.

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Grant SELECT on V$ Views

Grant SELECT on V$ views to allow non-admin database users to query SYS-owned V$ views (dynamic performance views) such as V$INSTANCE or V$SESSION.

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How to Find out Your Oracle Database Version

Three ways to find out your Oracle database version in SQL and PL/SQL: using V$VERSION, V$INSTANCE, or DBMS_DB_VERSION constants.

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UNPIVOT in Oracle 11G to Select Columns As Rows

You can easily transpose table columns to rows in Oracle 11G+ using the UNPIVOT clause is SQL. A comparison of the pre-11G DECODE solution with the 11G+ UNPIVOT method.

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SQL to Select Rows Conditionally Based On Column Value

SQL solution to select rows conditionally based on column value – for example, a priority column tagged to a set of rows, with a requirement to select only the rows with top priority.

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SQL to Find Master Records with Identical Detail Records

SQL to find those records in the master table that have identical detail records in a child table.

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Replace Duplicates in ID Column with Unique Values

A solution to the requirement of replacing only the duplicate IDs with unique values in a database table, and letting everything else stay untouched.

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The Curious Case of The Missing ORA-00904

What’s worse than an error that shows up when you don’t expect it? An error that does NOT show up when you totally expect it. Witness “ORA-00904: invalid identifier” playing truant.

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Hierarchical Data in a Relational Table

Flatten Hierarchical Data using a Single SQL

Single Oracle SQL to find and flatten hierarchical data stored in a table, using a combination of SYS_CONNECT_BY_PATH and regular expressions.

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LISTAGG for Converting Rows to Comma-Separated String

Oracle built-in function LISTAGG lets you concatenate multiple rows of data into a single delimiter-separated string. No more of those circuitous MAX(SYS_CONNECT_BY_PATH) or STRAGG solutions of the pre-Oracle 11G R2 days!

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