How to write sql statement in oracle

Writing Oracle SQL statements requires following the following steps: 1. Connect to the database; 2. Select the columns to be retrieved; 3. Specify conditions (optional); 4. Sort the results (optional); 5 . Limit the number of results (optional); 6. Use aggregate functions (optional); 7. Use subqueries (optional); 8. Use joins (optional).

How to write SQL statements in Oracle

Oracle SQL (Structured Query Language) is a powerful Tools for retrieving, manipulating, and updating data from Oracle databases. To write a valid SQL statement, you need to follow these steps:

1. Connect to the database

<code class="oracle">CONNECT username/password@database_name;</code>

2. Select the columns to retrieve

<code class="oracle">SELECT 列名
FROM 表名;</code>

3. Specify conditions (optional)

Use the WHERE clause to filter the query:

<code class="oracle">SELECT 列名
FROM 表名
WHERE 条件;</code>

4. Filter the results Sort (optional)

Use the ORDER BY clause to sort the results:

<code class="oracle">SELECT 列名
FROM 表名
ORDER BY 列名 ASC/DESC;</code>

5. Limit the number of results (optional)

Use LIMIT clause to limit the number of retrieved results:

<code class="oracle">SELECT 列名
FROM 表名
LIMIT 行数;</code>

6. Use aggregate functions (optional)

Aggregation functions (such as SUM, COUNT, AVG ) can perform calculations on data:

<code class="oracle">SELECT 聚合函数(列名)
FROM 表名
GROUP BY 分组列;</code>

7. Using subqueries (optional)

Subqueries are queries nested in the main query and are used for retrieval Intermediate results for the main query:

<code class="oracle">SELECT 列名
FROM 表名
WHERE 条件 IN (SELECT 列名 FROM 子查询);</code>

8. Using joins (optional)

Connections are used to retrieve data from multiple tables:

<code class="oracle">SELECT 列名
FROM 表名1 JOIN 表名2 ON 连接条件;</code>

Example:

Here's how to retrieve the names and salaries of all employees from the "EMP" table:

<code class="oracle">SELECT ename, sal
FROM emp;</code>

Here's how to sort the results in descending order of salary Sorting:

<code class="oracle">SELECT ename, sal
FROM emp
ORDER BY sal DESC;</code>

Here's how to use a subquery to find employees with above-average salaries:

<code class="oracle">SELECT ename
FROM emp
WHERE sal > (SELECT AVG(sal) FROM emp);</code>

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