sql语法摘要（SQL syntax summary）.docVIP

sql语法摘要（SQL syntax summary） Float 32 bit real number. Double 64 bit real number. Char (n) N string of length n cannot exceed 254. Varchar (n) A string whose length is not fixed and its maximum length is n, and N must not exceed 4000. Graphic (n) Like char (n), but its unit is two characters double-bytes, and N cannot exceed 127. This form is for A font that supports two character lengths, such as Chinese characters. Vargraphic (n) A two character string of variable length and its maximum length is n, and N must not exceed 2000. Date Contains year, month, date. Time It contains hours, minutes, seconds. Timestamp It includes year, month, day, hour, minute, second, 1/1000 seconds. Three. Data manipulation DML (Data, Manipulation, Language) After the data is defined, the following is the operation of the data. Data manipulation is nothing more than adding data (insert), query data (query), changing data (update), and deleting data (delete) in four modes, respectively, introducing their syntax as follows: 1, increase information: INSERT, INTO, table_name (column1, column2,...) ValueS (value1, Value2,...) Explain： 1. if the column system is not specified, the data is filled in the column order in the form. The data form of the 2. column must be consistent with the data filled. 3.table_name can also be a landscape view_name. INSERT, INTO, table_name (column1, column2,...) SELECT, columnx, columny,... FROM, another_table Explanation: you can also fill in the data from another table through a sub query (subquery). 2, query data: Basic query SELECT, column1, columns2,... FROM table_name Explanation: list all of the table_names specific column data SELECT * FROM table_name WHERE column1 = XXX [AND column2 yyy] [OR column3 zzz] Three) cross connect The cross connection does not take the WHERE clause, which returns the Descartes product of all data rows of the two tables being connected and returns the number in the result set The rows are equal to the number of rows in the f