Let's talk about Oracle query format

With the advent of the information age, data has become an important resource for enterprise management. As an efficient and reliable database management system, Oracle database is increasingly widely used in enterprise database applications. SQL query is an essential skill when using Oracle database. The format of SQL query also plays an important role in improving query efficiency. This article will explain the Oracle query format.

1. SQL regular query format

SQL regular query format is the most basic query format in the Oracle database. It consists of three keywords: SELECT, FROM and WHERE. SELECT is followed by the query column, FROM is the query table, and WHERE is followed by the query conditions.

For example: SELECT name, age FROM student WHERE age = 18;

The data column after the SELECT keyword can be a specific column name, or it can be a unified symbol (*), which means Query all columns. The data table after the FROM keyword needs to be filled in according to the actual situation. Generally, the name of the table to be queried needs to be specified. The data columns after the WHERE keyword are some qualifications, which can be numbers, text or other comparison symbols.

2. SQL query operator format

In SQL query, we can also use some operation symbols to perform query operations. Commonly used operators are: LIKE, IN, NOT IN, BETWEEN, IS NULL, etc. These operators can be used to query data of types such as strings, numbers, and dates.

For example: SELECT * FROM table WHERE name LIKE 'A%';

In the above example, we used the LIKE operator to query all name values ​​starting with A. The % sign is a wildcard symbol that can be used to represent any number of numbers or characters.

3. SQL query sorting format

In actual query operations, we may want the query results to be displayed in a specific way. At this time, the sorting operation is very important. In Oracle database, we can use the ORDER BY keyword to perform sorting operations. By default, ORDER BY sorts the query results in ascending order, but we can also use the DESC keyword to sort in reverse order.

For example: SELECT * FROM student ORDER BY age DESC;

In the above example, we use the ORDER BY keyword to sort the query results in reverse order according to the age field.

4. SQL query grouping and aggregate function formats

In addition to sorting, operators and conventional query formats, Oracle database also provides powerful query functions such as grouping and aggregate functions. These functions are very useful in some statistical and analytical operations.

For example: SELECT age, COUNT(*) FROM student GROUP BY age;

In the above example, we used the GROUP BY keyword to group the data of students of the same age. Let’s do statistics together. At the same time, we also used the COUNT function to calculate the number of people in each age group.

5. SQL query connection format

In the Oracle database, there may be certain connections between different tables. At this time, we need to perform connection queries between tables. Connection queries between tables can be divided into inner joins, outer joins, self-joins, etc.

For example: SELECT * FROM table1 INNER JOIN table2 ON table1.key = table2.key;

In the above example, we use INNER JOIN to implement the inner join of the table, connecting table1 and table2 Data with the same key value are merged.

To summarize, the query formats in Oracle database are very rich and diverse. We can choose different query methods according to different situations to achieve efficient database query operations. Mastering these query formats is of great value for business management and decision-making.

The above is the detailed content of Let's talk about Oracle query format. For more information, please follow other related articles on the PHP Chinese website!