Oracle Skills

Inner join and WHERE clauses are used to filter rows from multiple tables in a SQL query, but they work slightly differently. An INNER JOIN combines rows from two or more tables based on a related column. It returns only the rows that have matching …

You can list all the columns in a table in Oracle by querying the "user_tab_columns" data dictionary view. The following SQL query can be used: SELECT column_name FROM user_tab_columns WHERE table_name = 'table_name'; You can also …

There are a couple of ways to create a copy of an Oracle table without copying the data: 1. Using the CREATE TABLE AS SELECT statement (CTAS): CREATE TABLE new_table_name AS SELECT * FROM original_table_name WHERE 1=0; This query will create a new t…

There are several ways to find duplicate values in a table in Oracle: 1. Using the GROUP BY clause and the HAVING clause: SELECT column1, column2, ..., COUNT(*) FROM table_name GROUP BY column1, column2, ... HAVING COUNT(*) > 1; This query will r…

The ORA-12514 is a standard Oracle error that occurs when attempting to connect to a database using SQL*Plus or another Oracle client tool. It typically indicates that the client cannot connect to the listener on the specified host and port and that…

In Oracle SQL, you can use the "UPDATE" statement to update a table with data from another table. The basic syntax for the statement is as follows: UPDATE target_table SET target_table.col1 = source_table.col1,     target_table.col2 = sour…

In Oracle, you can use the "MERGE" statement to perform an UPSERT, which updates a row in a table if it already exists or inserts a new row if it does not. The basic syntax for the statement is as follows: MERGE INTO target_table USING sou…

You can use the UNION operator to combine the results of multiple SELECT COUNT(*) statements to get the total count of rows across multiple tables. The basic syntax is as follows: SELECT COUNT(*) FROM table1 UNION SELECT COUNT(*) FROM table2 UNION S…

Oracle databases have a boolean data type, but it is called "BOOLEAN" rather than "BOOL." The boolean data type can have only two possible values: true or false. You can use the "BOOLEAN" data type in SQL statements to …

In Oracle, a user and a schema are related but distinct concepts. A user is a specific account created and managed by a database administrator (DBA). Each user has a unique name and password and can be granted various system privileges, such as crea…

The best way to do a multi-row insert in Oracle is to use the INSERT ALL statement. This statement allows you to insert multiple rows into a table or multiple tables at once using a single command. The syntax for the INSERT ALL statement is as follo…

You can check if a table exists in Oracle by querying the data dictionary. The data dictionary is a set of tables and views that provide information about the database schema and objects. You can use the "ALL_TABLES" view to check if a tab…

In Oracle, views and materialized views are both database objects that can be used to present a customized version of data from one or more tables, but they have some important differences: A view is a virtual table that is defined by a SELECT state…

Liquibase is a database migration tool that helps manage changes to a database schema. The liquibase lock is a mechanism that prevents multiple users or processes from modifying the database schema simultaneously, which could lead to conflicts or da…

There is no direct combination of the "LIKE" and "IN" operators in SQL. However, you can use the "LIKE" operator within a subquery that uses the "IN" operator to achieve a similar result. Here is an example of…

In Oracle, you can create a column with AUTO_INCREMENT functionality by using a sequence and a trigger.  A sequence is a database object that generates unique integers and can be used to create unique values for the column. A trigger is a database o…

In Oracle, you can use the "UPDATE" statement with an "INNER JOIN" clause to update data in one table based on data in another. The "INNER JOIN" clause combines rows from two or more tables based on a related column bet…

Oracle SQL Developer is a free and fully-featured integrated development environment (IDE) specifically designed for working with Oracle databases. It provides various database development tools, including generating an entity-relationship (ER) diag…

Oracle is a powerful and feature-rich relational database management system (RDBMS) that provides a wide range of capabilities to help organizations manage, analyze, and gain insights from their data. Here are some of the key features and capabiliti…

In Oracle, you can limit the number of rows returned by a query by using the "ROWNUM" keyword in your query's "WHERE" clause. The "ROWNUM" keyword assigns a unique number to each row in the result set, starting at 1…

In Oracle, both VARCHAR and VARCHAR2 are datatypes used to store variable-length character strings, but there is a slight difference between them. The main difference between VARCHAR and VARCHAR2 is that VARCHAR can store up to 2000 data, while VARC…

A foreign key is a column or a set of columns in a table that establishes a link between the data in two tables. The value in the foreign key column(s) must match the primary key column(s) value in the related table. A foreign key column can be defi…