国外主机测评 - 国外VPS，国外服务器，国外云服务器，测评及优惠码
查询指定数据表是一个非常普遍的需求，以Oracle数据库作为数据库的例子，下面将给出具体的查询步骤，以供参考。
1. 进入Oracle数据库，查看所有的表名
当你连接上Oracle数据库以后，若要查看一共有哪些表，可以使用以下代码：
SELECT table_name FROM user_tables
用这条语句可以查出当前用户下的所有数据表，如果想知道某个指定用户的表名，可以改下表名，比如某用户为SCOTT，则可以使用：
SELECT table_name FROM scott.user_tables
2. 用sql查询指定数据表
当找到了指定的表名以后，就可以用SQL查询它的内容了，通常情况下用的就是SELECT语句：
SELECT * FROM tablename
用这个语句可以选择出一张表的所有列（全部字段），如果只想查询指定几个列，可以改写成：
SELECT column1, column2, column3 FROM tablename
即指定具体想查询的字段，也可以根据字段值进行条件查询：
SELECT * FROM tablename WHERE column1 = value1
比如上面，就是要查询某一列中符合某个值的所有记录。
3. 常用Oracle查询语句
除了上面提到的一些基本语句以外，Oracle中还有很多查询函数，这些函数可以用来查询指定的记录数据：
（1）ORDER BY：可以按照指定的字段（列）进行排序：
SELECT * FROM tablename ORDER BY column1
（2）GROUP BY：可以将查出的结果根据指定的字段（列）进行分组：
SELECT COUNT( column1 ) FROM tablename GROUP BY column1
（3）HAVING：是使用GROUP BY后的条件语句，一般与GROUP BY搭配使用：
SELECT SUM( column1 ) FROM tablename GROUP BY column1 HAVING SUM( column1 ) > value
以上，就是本指南关于如何查询Oracle中指定数据表的大致内容，使用上述方法可以实现最基本的查询功能，只要熟悉常用函数，就可以根据自己的需求来查询出符合要求的数据。
—————————————-
Simple English version:
Query the specified table is a very common need, using Oracle database as an example, the following specific query steps will be given for reference.
1. Log in to the Oracle database and view the names of all tables
Once you are connected to the Oracle database, if you want to see which tables are available, you can use the following code:
SELECT table_name FROM user_tables
This statement can query all the data tables under the current user. If you want to know the table name of a specific user, you can change the table name, for example, if the user is SCOTT, you can use:
SELECT table_name FROM scott.user_tables
2. Use the SQL query to specify the table
Once the specific table name is found, the content can be queried with SQL, usually using the SELECT statement:
SELECT * FROM tablename
This statement can select all columns (all fields) of a table. If you only want to query a few columns, you can modify it:
SELECT column1, column2, column3 FROM tablename
That is, specify the specific fields to be queried, and also can query according to the field value:
SELECT*FROM tablename WHERE column1 = value1
For example, above, it is to query all records in a column that meet a certain value.
3. Common Oracle query statement
In addition to the basic statements mentioned above, there are many query functions in Oracle, which can be used to query the specified record data:
(1) ORDER BY: Can sort by the specified field (column):
SELECT * FROM tablename ORDER BY column1
(2) GROUP BY: Can group the query results according to the specified field (column):
SELECT COUNT(column1) FROM tablename GROUP BY column1
(3) HAVING: Is the condition statement after using GROUP BY. It is usually used with GROUP BY:
SELECT SUM(column1) FROM tablename GROUP BY column1 HAVING SUM(column1) > value
Above is the general content of this guide on how to query specified tables in Oracle. By using the above methods, the most basic query function can be achieved. As long as familiar with the common functions, you can query the data that meets the requirements according to your own needs.
