What does * represent in sql
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The * symbol in SQL is a wildcard character, which means it can match any character sequence. Common uses include: Select all columns: SELECT * FROM table_name; Select a specific column range: SELECT * FROM table_name WHERE column_name BETWEEN start_value AND end_value ;Join table: SELECT * FROM table1 INNER JOIN table2 ON table1.id = table2.id;Search mode: SELECT * FROM table
SQL Medium The * symbol
In SQL query statements, the symbol represents a wildcard character, which can match any character sequence. This enables the notation to be used for a wide range of query operations.
Usage
- symbol has the following common uses:
-
Select all columns:
SELECT * FROM table_name;
This will select all columns of all records in the table.
-
Select a specific column range:
SELECT * FROM table_name WHERE column_name BETWEEN start_value AND end_value;
This will select the table All records within a specific column value range.
-
Join table:
SELECT * FROM table1 INNER JOIN table2 ON table1.id = table2.id;
This Two tables will be joined, using the specified join conditions.
-
Search mode: When used with the LIKE operator, the * symbol can represent any number of characters. For example:
SELECT * FROM table_name WHERE column_name LIKE '%pattern%';
This will select all records in column_name that contain the pattern character sequence.
- Aggregation functions:
- notation can be used with aggregate functions such as SUM() and COUNT():
<code>SELECT SUM(*) FROM table_name;</code>
This will calculate the sum of the specified column across all records in the table.
Other Notes
- symbols cannot match line breaks.
- In some cases, you can use the % symbol as a wildcard character, which behaves similarly to the * symbol.
- In regular expressions, the * symbol has a different meaning and means repeating the previous element zero or more times.
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