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What is a primary key?
A primary key is a column or set of columns that uniquely identifies a row in a table. It’s created on a table and ensures that the values in that column or columns must be unique and not NULL. This is often done using some kind of numeric ID field but doesn’t have to be.
A primary key is a column or set of columns that uniquely identifies a row in a table. It’s created on a table and ensures that the values in that column or columns must be unique and not NULL.
This is often done using some kind of numeric ID field but doesn’t have to be.
See lessWhat’s the difference between a view and a materialized view?
A view is simply an SQL query that is stored on the database, without the results. Every time a view is queried, this definition of the view’s query is run. If the underlying tables have been updated, the view will load these results. A materialized view is a query where the results have been storedRead more
A view is simply an SQL query that is stored on the database, without the results. Every time a view is queried, this definition of the view’s query is run. If the underlying tables have been updated, the view will load these results.
A materialized view is a query where the results have been stored in a permanent state, like a table. If the underlying tables are updated, then by default, the materialized views are not updated.
See lessWhat is a view? When would you use one?
A view is a database object that allows you to run a saved query to view a set of data. You create a view by specifying a SELECT query to be used as the view, and then the view can be queried just like a table. There are several reasons to use a view, such as to improve to security, create a layer oRead more
A view is a database object that allows you to run a saved query to view a set of data. You create a view by specifying a SELECT query to be used as the view, and then the view can be queried just like a table.
There are several reasons to use a view, such as to improve to security, create a layer of abstraction between the underlying tables and applications, and to simplify queries.
See lessWhat is the purpose of the IN keyword?
The IN keyword allows you to check if a value matches one of a range of values. It’s often used with subqueries that return more than one row.
The IN keyword allows you to check if a value matches one of a range of values. It’s often used with subqueries that return more than one row.
See lessWhat is the purpose of the BETWEEN keyword?
The BETWEEN keyword allows you to check that a value falls in between two other values in the WHERE clause. It’s the same as checking if a value is greater than or equal to one value, and less than or equal to another value.
The BETWEEN keyword allows you to check that a value falls in between two other values in the WHERE clause.
It’s the same as checking if a value is greater than or equal to one value, and less than or equal to another value.
See lessWhat are the different DML commands in SQL? Give a description of their purpose.
Different DML commands in SQL: SELECT: retrieve or view data from the database INSERT: add new records to a table UPDATE: change existing records in a table DELETE: removes data from a table MERGE: performs an UPSERT operation, also known as insert or update. CALL: runs a PL/SQL procedure or Java prRead more
Different DML commands in SQL:
- SELECT: retrieve or view data from the database
- INSERT: add new records to a table
- UPDATE: change existing records in a table
- DELETE: removes data from a table
- MERGE: performs an UPSERT operation, also known as insert or update.
- CALL: runs a PL/SQL procedure or Java program
- EXPLAIN PLAN: explains the way the data is loaded
- LOCK TABLE: helps control concurrency
See lessWhat are the different DDL commands in SQL? Give a description of their purpose.
Different DDL commands in SQL: CREATE: creates objects in the database ALTER: makes changes to objects in the database DROP: removes objects from the database TRUNCATE: deletes all data from a table COMMENT: adds comments to the data dictionary RENAME: renames an object in the database
Different DDL commands in SQL:
- CREATE: creates objects in the database
- ALTER: makes changes to objects in the database
- DROP: removes objects from the database
- TRUNCATE: deletes all data from a table
- COMMENT: adds comments to the data dictionary
- RENAME: renames an object in the database
See lessWhat is the difference between SQL and T-SQL?
SQL is the language used to query databases. You run a query, such as SELECT or INSERT, and get a result. T-SQL stands for Transact-SQL and is a language and set of extensions for SQL Server that allows for further programming logic to be used with SQL.
SQL is the language used to query databases. You run a query, such as SELECT or INSERT, and get a result.
T-SQL stands for Transact-SQL and is a language and set of extensions for SQL Server that allows for further programming logic to be used with SQL.
See lessWhat is the difference between SQL and PL/SQL?
SQL is the language used to query databases. You run a query, such as SELECT or INSERT, and get a result. PL/SQL stands for Procedural Language/Structured Query Language. It’s Oracle’s procedural language and is built on top of SQL. It allows for more programming logic to be used along with SQL.
SQL is the language used to query databases. You run a query, such as SELECT or INSERT, and get a result.
PL/SQL stands for Procedural Language/Structured Query Language. It’s Oracle’s procedural language and is built on top of SQL. It allows for more programming logic to be used along with SQL.
See lessWhat is the difference between SQL, Oracle, MySQL, and SQL Server?
SQL is the name of the language used to query databases and follows a standard. Oracle, MySQL, and SQL servers are different implementations or versions of a database management system, which implement the SQL standard and build on it in different ways. Oracle database is targeted at large companiesRead more
SQL is the name of the language used to query databases and follows a standard. Oracle, MySQL, and SQL servers are different implementations or versions of a database management system, which implement the SQL standard and build on it in different ways.
See lessOracle database is targeted at large companies, SQL Server is owned by Microsoft, and MySQL is owned by Oracle but targeted toward smaller companies and systems.