A key is a column or expression on which you can build an index. Follow these guidelines for choosing keys to index: Consider indexing keys that are used frequently in WHERE clauses. Consider indexing keys that are used frequently to join tables in S…
When a table column is defined with the implicitly hidden attribute, that column is unavailable unless it is explicitly referenced. For example, if a SELECT * query is run against a table, implicitly hidden columns are not returned in the result tabl…
DimProduct DimSubcategory Dimcategory productpk subcategorypk categorypk sku subcategoryName categoryName productName categorypk subcategorypk Snow flake schema has one weakness, Take the product dimension sample, its has subcategory attribute. If we…
Removing Columns time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output You are given an n × m rectangular table consisting of lower case English letters. In one operation you can completely remo…
Alter Table/Partition/Column Alter Table Rename Table Alter Table Properties Alter Table Comment Add SerDe Properties Alter Table Storage Properties Additional Alter Table Statements Alter Partition Add Partitions Dynamic Partitions Rename Partition…
Hive Data Definition Language Hive Data Definition Language Overview Create/Drop/Alter Database Create/Drop/Truncate Table Alter Table/Partition/Column Create/Drop/Alter View Create/Drop/Alter Index Create/Drop Function Create/Drop/Grant/Revoke Roles…
drop后的表被放在回收站(user_recyclebin)里,而不是直接删除掉.这样,回收站里的表信息就可以被恢复,或彻底清除. 1.通过查询回收站user_recyclebin获取被删除的表信息,然后使用语句flashback table <user_recyclebin.object_name or user_recyclebin.original_name> to before drop [rename to <new_table_name>]; 将回收站里的表恢复为原名称…
一.drop表 执行drop table xx 语句 drop后的表被放在回收站(user_recyclebin)里,而不是直接删除掉.这样,回收站里的表信息就可以被恢复,或彻底清除. 通过查询回收站user_recyclebin获取被删除的表信息,然后使用语句 flashback table <user_recyclebin.object_name or user_recyclebin.original_name> to before drop [rename to <new_tabl…
The easiest way to create a copy of a table is to use a Transact-SQL command. Use SELECT INTO to extract all the rows from an existing table into the new table. The new table must not exist already. The following example will copy the Customers table…
C. Removing Columns time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output You are given an n × m rectangular table consisting of lower case English letters. In one operation you can completely r…
apple=# create table test(id integer, info text); CREATE TABLE apple=# insert into test select generate_series(1, 100000), md5('test'); INSERT 0 100000 apple=# select * from test limit 1; id | info ----+---------------------------------- 1 | 098f6bcd…
