Let's talk about Oracle's commonly used query and judgment statements

Oracle query judgment

Oracle is a widely used relational database system. It has efficient data storage and query capabilities and has become one of the indispensable tools in enterprise management. When using Oracle for data query, we need to filter the required data through judgment statements. In this article, we will introduce the relevant knowledge of Oracle queries and commonly used query judgment statements.

1. Basic query statement

In Oracle, we use the SELECT statement for data query. Its basic form is as follows:

SELECT column1, column2, ... FROM table_name ;

Among them, column represents the column to be queried, and table_name represents the name of the table to be queried. For example, to query all data in a student table, you can use the following statement:

SELECT * FROM Student;

This will return a table containing all student information.

2. Query judgment statements

In addition to the basic SELECT statement, we can also use some judgment statements to filter the required data. The following are commonly used query judgment statements:

(1) WHERE statement

The WHERE statement is used to select data rows that meet specific conditions. For example, if we want to select all students older than 20 years old in the student table, we can use the following statement:

SELECT * FROM Student WHERE age > 20;

The result table returned at this time Only information about students older than 20 years old will be included.

(2) LIKE statement

The LIKE statement is used for fuzzy matching queries and is often used to search for data containing specific characters or strings. For example, to query all students whose names contain "Li", we can use the following statement:

SELECT * FROM Student WHERE name LIKE '%Li%';

Note that wildcards are used here "%" means matching any number of characters. The results of such a query will include information about all students whose names contain "Li".

(3) BETWEEN statement

The BETWEEN statement is used to select data rows that meet a certain interval condition. The interval is represented by two values ​​(including these two values). For example, if we query students between the ages of 20 and 25, we can use the following statement:

SELECT * FROM Student WHERE age BETWEEN 20 AND 25;

(4) IN statement

The IN statement is used to select from a set of candidate values, that is, the result can be returned as long as any one value is satisfied. For example, if we query the information of all students with student IDs 1,2,3, we can use the following statement:

SELECT * FROM Student WHERE id IN (1,2,3);

( 5) NOT statement

The NOT statement is used to negate a certain condition, that is, to select data rows that do not meet a certain condition. For example, if we query the information of students who are not 20 years old and under, we can use the following statement:

SELECT * FROM Student WHERE NOT age <= 20;

3. Logical operators

When using query judgment statements, we also need to use logical operators AND, OR and NOT to connect different query conditions. For example, if we query the information of all students aged between 20 and 25 and living in Beijing or Shanghai, we can use the following statement:

SELECT * FROM Student WHERE age BETWEEN 20 AND 25 AND (city='Beijing ' OR city='Shanghai');

When multiple query conditions exist, the priority of logical connectors requires attention. We can enforce priority by using parentheses.

4. Summary

Oracle query judgment is an important means to achieve data screening. We need to be proficient in the use of common query judgment statements and logical operators, and use them flexibly in practical applications to improve the efficiency of data queries.

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