How to run a select statement on SQL Plus to view basic database information

select * from v$database;View the current database.

The display cursor function in the Oracle 10G DBMS xplan package is different from the display function, the display cursor is used to display the real execution plan of the SQL statement, and in most cases, the display of the real execution plan is helpful to better analyze the whole process of the SQL statement, especially the real-time cost of running the SQL statement. This is determined by comparing the estimated IO with the actual IO cost.

Problems with SQL statements, such as the lack of statistics, the number of SQL statements executed, and the selection of appropriate connection methods based on the size of the actual intermediate result set. This article is just about it.

I've looked at a lot of SQL query statements on the Internet, but I feel like those are very simple, can anyone give me some advanced SQL interview questions I've done, I wrote the table and added the test data, if you're interested, try one.

Oracle.

Oracle appends a comment on a table field with a comment on table comment on column.

create table "mr_dept" (

dept_id" number not null ,parent_id" number,dept_name" char(20) not null ,status" number default 1 not null ,primary key ("dept_id")

comment on table "mr_dept" is 'Department table';

comment on column "mr_dept"."dept_id" is 'Department number';

comment on column "mr_dept"."parent_id" is 'Parent department number';

comment on column "mr_dept"."dept_name" is 'Department name';

comment on column "mr_dept"."status" is 'Status';

After the remarks are added, how can I search for them in the query?

Remarks in the query table.

select

table_name,table_type,comments

fromuser_tab_comments

wheretable_name = 'mr_dept;

Comment information for the query field.

select

table_name,column_name,comments

fromuser_col_comments

wheretable_name = 'mr_dept;

You just need to do it.

select * from user_tab_comments;

What kind of database is it?

select [field to be searched for copy] from [table name] where [specified bai query conditions].

There is a need to remember.

What is explained is that if there are multiple conditions, you need to use and to join each query condition, and if you need to sort, the syntax is:

select [field to be queried] from [table name] where [specified search conditions].

order by [fields to group].

Description: SQL Server database can be copied and queried with conditions to achieve the display of data records that meet the query conditions. The query syntax is:

select * from table name where field name = condition (syntax description: the * sign after select represents all fields displayed.) If the condition is a character condition, you need to use single quotation marks, if it is an int type, you need to use two query methods:

1. The syntax of the complete conditional query is as follows: select * from table name where field name = condition.

Query statement: select * from user user where dname='Administrators'

2. The query syntax of fuzzy query conditions is: select * from table name where field name like'%Condition%' 。The condition here only needs one of the characters to be able to match the match in the field.

Query statement: select * from user user where dadd like'% more expensive'

select *from table_name

where is followed by the condition that you specify, such as name='Bruce Lee'Something like that.

Hello Lao Tie.

select * from TableName Where Condition...

Note here:

isql -u natuser -p zjtt@nat -s natdb <

That is, redirect the query results to a file.

2 To output to variables.

isql -u natuser -p zjtt@nat -s natdb <·3 If you want to output to a variable in a loop, you can refer to the read method by analogy.