Introduction to Chapter Structured Query 8 Language (SQL) | Class 11 Informatics Practices Notes

8.6 SQL FOR DATA QUERY

The SELECT statement in SQL is used to retrieve data from one or more tables in a database. It allows users to specify the columns to be retrieved and conditions to filter records. The basic syntax is 'SELECT attribute1, attribute2, ... FROM tablename WHERE condition;'. The WHERE clause is optional and is used to specify conditions for filtering data. SQL supports various operators in WHERE clause such as =, <, <=, >, >=, !=, AND, OR, NOT to combine multiple conditions. The DISTINCT keyword is used to eliminate duplicate records in the output. The ORDER BY clause sorts the output in ascending (default) or descending order based on specified columns. SQL also supports pattern matching using the LIKE operator with wildcards '%' (zero or more characters) and '_' (single character). NULL values can be checked using IS NULL and IS NOT NULL. Aliases can be used to rename columns in the output using the AS keyword. This section uses the OFFICE database example with EMPLOYEE table to demonstrate various SELECT queries including retrieving specific columns, renaming columns, filtering with WHERE, using DISTINCT, BETWEEN, IN, and pattern matching with LIKE. Understanding these querying capabilities is essential for effective data retrieval from relational databases.

📊 Diagram: Tables 8.8 and others showing EMPLOYEE data; Figure 8.7 comparing OR and AND operators in queries

🧪 Activity: Activity 8.8: Compare outputs of queries using OR and AND operators to understand their differences.

🔗 Connection: This section covers querying data and leads to the next section on data updation and deletion.

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