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When querying the data in the oracle database, it is usually not a condition to filter out the desired results, so the and and or join operators come in handy when you need to specify multiple complex filter conditions.

Basic operator single quotation marks ('): in Oracle, only single quotation marks should be used to enclose text and characters and dates, not numbers (including single and double quotation marks). Double quotation marks ("): single and double quotation marks have different meanings in Oracle. Double quotation marks are used to enclose column aliases that contain specific characters or spaces. Double quotation marks are also used to put text apostrophes ('): in Oracle, apostrophes can also be written as two single quotes adjacent to each other. To find all supplier names with apostrophes in the middle of the supplier name, you can write code like this: select * from l_suppliers where supplier_name like'%'& symbol: in Oracle, the & symbol is often used to indicate a variable. For example, & fox is a variable, a slightly different one & & fox. Whenever & fox appears in an Oracle script, you are asked to provide a value for it. With & & fox, you only need to provide the value of the variable to & & fox when it first appears. If you want to use the & symbol as an ordinary symbol, you should turn off this feature. To turn off this feature, run the following command: set define off, which is a SQLplus command, not a SQL command. SQLplus configures the environment in which SQL runs in Oracle. Double vertical lines (): Oracle uses double vertical bars to represent string concatenation functions. An asterisk (*): select means to select all columns, and count () means to calculate all rows, indicating 0 or any number of characters when representing wildcards. Forward slash (/): in Oracle, used to terminate a SQL statement. More precisely, it means "run the SQL code that is now in the buffer". The forward slash is also used as a separator. Multi-line comment: / * / does not mean: there are many ways to express:! =, ^ =, not xxx=yyy, not (xxx=yyy) operators for where comparison conditions

Equal to: =, > =, including: in, not in, exists, not exists range: between... And, not between. And matching test: like, not likeNull test: is null, is not null Boolean link: and, or, not

Wildcard character

In the where clause, wildcards can be used in conjunction with like conditions. In Oracle:% (percent sign): used to represent any number of characters, or there may be no characters at all. _ (underscore): indicates the exact unknown character. (question mark): used to indicate the exact unknown character. # (pound sign): used to indicate the exact Arabic numeral, 0 to 9. [amurd] (square brackets): used to indicate a range of characters, in this case from a to d.

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