import MySQLdb # 连接到MySQL数据库 conn = MySQLdb.connect(host='localhost', user='username', passwd='password', db='database') cursor = conn.cursor() # 查询表的列 cursor.execute("DESCRIBE table_name") columns = cursor.
The SELECT UNIQUE construct is an Oracle-only SQL statement. It is equivalent to SELECT DISTINCT. SyntaxThe syntax for SELECT UNIQUE is as follows:SELECT UNIQUE "column_name" FROM "table_name";ExampleWe use the following table for our example. Table Store_Information ...
-- select the unique ages from the Customers tableSELECTDISTINCTageFROMCustomers; Run Code Here, the SQL command selects only the unique values of age from theCustomerstable. Syntax of SQL SELECT DISTINCT SELECTDISTINCTcolumn1, column2 ...FROMtable; Here, column1, column2, ...are the table...
So far we have used the select statement to retrieve all the records in a table regardless if some values repeat or not. If you wish, you can use the DISTINCT keyword to remove duplicates from your results. For instance if you wanted to just return a unique list of employees’ titles yo...
mysql> SELECT t1.name AS '姓名',t1.teacher_id '老师ID' FROM student AS t1 WHERE id % 2 = 1 LIMIT 3; 8>.当多个表中有相同的字段名,且需要查询出来时,需要在SELECT_EXPR中使用tbl_name.column_name 来显视指定要查询哪个表的字段 9>.查看另外的数据库的表数据 ...
在开始之前,我们首先需要导入一个数据库来测试我们的转换方法。你可以使用以下SQL语句在SQL Server中创建一个测试表: CREATETABLETestTable(ID uniqueidentifierPRIMARYKEY,Name nvarchar(50))INSERTINTOTestTable(ID,Name)VALUES('2C4E76A0-CE8E-4CB6-80DA-4D9A889DF880','John') ...
CREATE UNIQUE INDEX UIX_TestTable_Val ON TestTable(Val) GO INSERT INTO TestTable(Val) VALUES(10),(20),(30),(40),(50) GO SELECT * FROM TestTable A database with a single table is created. The table has indexes, constraints, and contains sample data: ...
SELECT 语句的基本语法如下所示:SELECT 第 1 列,第 2 列,...FROM source_table;要在结果集中显示表中的所有列,请在 SELECT 之后使用符号“*”。同样,您可以设置其他标志,例如仅返回唯一行的选项(使用 ONLY UNIQUE)修饰符。...组合 SQL SELECT 和 INSERT 语句包含嵌套 SELECT 语句的 INSERT 语句允许您使用 ...
The operator applicable to a column depends on column's data type. For example, arithmetic operators will not fit for character literal values. For example,SELECT employee_id, sal * 12 ANNUAL_SAL FROM employees; The above query contains the arithmetic expression (sal * 12) to calculate annual...
Joinin连接): A join operation combines data from two or more tables based on one or more common column values. A join operation enables an information system user to process the relationships that exist between tables. The join operation is very powerful because it allows system users to invest...