Understanding how SQL works can help you create better queries, and can make it easier for you to understand how to fix a query that is not returning the results that you want. This is one of a set of articles
DQL is another important command in SQL. This mainly helps to perform queries on data. The main motive behind this is to get some schema-related queries. These DQL commands include the SELECT statement. These SELECT commands are used to retrieve data from the database. This result will get ...
Refresh queries the database for the current details about the selected object (for example, a connection or just a table). Apply Filter restricts the display of objects using a filter that you specify. For example, you can right-click the Tables node and specify a filter of EM% to see ...
This topic covers the main Oracle SQL Developer concepts, and explains how to use the major SQL Developer features.
Connect to a SQL Server instance in SSMS. Create and query a SQL Server database in SSMS running basic Transact-SQL (T-SQL) queries.
UNION: Union operation combines results from two queries, and removes duplicates. Except: Except operation returns rows from the first query that are not in the second query. INTERSECT: Intersect returns rows that are common to both queries. 14. What is a subquery? A subquery is a query nest...
Example The following example creates a unique index on the MyCustomers table. Copy CREATE TABLE MyCustomers (CustID int, CompanyName nvarchar(50)); CREATE UNIQUE INDEX idxCustId ON MyCustomers (CustId); Concepts Query Performance Tuning (SQL Server Compact) Database ObjectsEnglish...
Understand the characteristics of the columns used in the queries. For example, an index is ideal for columns that have an integer data type and are also unique or non-null columns. For columns that have well-defined subsets of data, you can use a filtered index in SQL Server 2008 (1...
Statement objects allow you to execute basic SQL queries and retrieve the results through the ResultSet class, which is described later. To create a Statement instance, you call the createStatement() method on the Connection object you have retrieved using one of the DriverManager.getConnection()...
Components and concepts Statistics options When to create statistics When to update statistics 显示另外 2 个 Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics SQL database in Microsoft Fabric The Query Optimizer uses statistics to create query plans that imp...