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1. What is a window function? Window functions are also analysis functions. Oracle from 8.1 6 start to provide window function, which is used to calculate some aggregate value based on group, The window function specifies the data window size of the analysis function. The data window size may change with the change of rows. Unlike aggregat ...

1, Multi table query multi-table query   -- merge union   -- intersection intersect   -- subtraction minus The INTERSECT operator returns only the common rows of the two queries For example: SELECT orderno FROM order_master INTERSECT SELECT orderno FROM order_detail; The MINUS operator returns rows that appear in the sec ...

SQL master: add, modify, delete and query four sentence patterns SQL statement: a general standard for structured query statements in relational databases. Relational database (table): Mysql, Oracle, DB2, SqlServer, etc. (1) INSERT add statement (1.1) insert all fields Note: the added data must be consistent with the order, number and type ...

Oracle self study notes sorting (IV) 8, Functions 8.1 distinct When the keyword DISTINCT is followed by only one column 1, it represents the non duplicate data of the query result of a single field. When it is followed by multiple column values, it represents all the unique values of the query result composed of multiple fields, and the group ...

Chapter 4 SQL aggregate function COUNT (2) jurisdiction To use COUNT(*), you must have table level SELECT permissions on the specified table. To use count (column name), you must have column level SELECT permission on the specified column or table level SELECT permission on the specified table. You can determine whether the current user h ...

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catalogue 1. Many to one processing 1.1 database design 1.2 nested processing by query 1.3 nesting by result 2. One to many processing 2.1. Nesting by result 3. Summary 1. Many to one processing 1.1 database design Entity class: @Data @AllArgsConstructor @NoArgsConstructor public class Student { private int id; private S ...

multi-table query Table used in the example: emp table dept table Syntax: select * frome Table 1,Table 2, where condition; Tip: the condition of multi table query cannot be less than - 1 of the number of tables, otherwise the Cartesian product will appear, that is, the result is the number of rows in Table 1 * the number of rows ...

SQL statement operation_ MySQL core query 2 (multi table query) 1 foreign key constraints 1.1 foreign keys The foreign key refers to the field in the slave table corresponding to the primary key of the primary table (that is, there is A column in data table A, which points to the primary key of another data table B, and this column in da ...

catalogue 1, Environment construction 1. System planning 2. Configure DM ini 3. Configure dmmal ini 4. Configure dmmpp ctl 5. Run MPP 2, Problem solving 1. After starting two instances, start/ disql error  2. Common meter test 3. Temporary meter test 1, Environment construction Build a two node MPP cluster in linux environment ...