vt1

voltage containing a certain pulsating component. The voltage is converted into a square wave of the required voltage value, finally, the square wave voltage is converted into the required DC voltage by rectifying and filtering.The control circuit is a pulse width modulation. It consists of sampling devices, comparator, oscillator, pulse width modulation, reference voltage, and other circuits. This part of the circuit has been integrated, made into a variety of switching power supply integrated

Recently, we need to do some research on SQL query performance improvement, so we have studied the SQL statement solution process. I read it in the garden and wrote many related articles, with different focuses. This article is summarized on the mobile phone after reading various materials. It will detail the parsing process of each keyword of an SQL statement step by step. You are welcome to learn from each other. SQL statement parsing Sequence Simply put, an SQL statement is parsed in the fol

Recently, we need to do some research on SQL query performance improvement, so we have studied the SQL statement solution process. I read it in the garden and wrote many related articles, with different focuses. This article is summarized on the mobile phone after reading various materials. It will detail the parsing process of each keyword of an SQL statement step by step. You are welcome to learn from each other. SQL statement parsing Sequence Simply put, an SQL statement is parsed in the fol

Because of the recent need to do some research on the performance improvement of SQL query, I studied the solution of SQL statements. Read in the garden, we wrote a lot of related articles, we have different emphasis. This article is I read a variety of data after the phone summary, will be detailed, step-by-step about a SQL statement of each keyword parsing process, welcome to learn from each other. parsing Order of SQL statements Simply put, an SQL statement is parsed in the following order:

Tags: page operator declaration insert Block List add about reading notesFirst, about T-SQLT-SQL is an MS-SQL extension of the ANSI and ISO SQL standard, formally known as Transact-SQL, but is called T-SQL by a general programmer.Second, the logical query processing each stage 2.1 logical query Processing process overview2.2 Logical Query processing phase interpretation(1) From: Identifies the source table of the query and handles table operators. Each operator applies a series of sub-stages. eg

data, and the subquery does not actually return any data, but instead returns a value of TRUE or False--exists: Emphasizes whether to return the result set, does not require to know what to return--exists each row of the outer query table as a test, and if the result returned by the inner query takes a non-null value, the EXISTS clause returns TRUE, which can serve as the result row of the outer query, otherwise it cannot be a result.With VT1 as(sele

follows: From On JOIN WHERE GROUP by Having SELECT DISTINCT ORDER by LIMIT When these steps are executed, each step produces a virtual table that is used as input to the next step. These virtual tables are not available to callers (client applications or external queries). Only the table generated in the last step is returned to the caller. If you do not specify a clause in the query, the corresponding step is skipped.What each of the select pha

|ROLLUP} (7) having Having_condition> (Ten)ORDER by Order_by_list> Introduction to the Logical query processing phase From : performs a cartesian product (Cartesian product) (cross join) on the first two tables in the FROM clause, generating the virtual table VT1. On : apply an on filter to VT1. Only those lines that make OUTER (Join): If OUTER join is specified (relative to cross join or (INN

you do not include top, Why can't I use ORDER by? CREATE VIEW V as SELECT * from orders ORDER by orderid ; (wrong) CREATE VIEW V as Select TOP Ten * from Orders ORDER by ORDERIDNBSP; ; (pair) 3, Why can't aliases in the select list be used in the WHERE clause? select customerid as Id From Orders WHERE id>5; (wrong) 4. In a query statement that uses the GROUP BY clause, why is the column in the having or SELECT clause only a column in the GROUP BY clause or wrapped in an a

'), (' CCC ', ' Mike '), [' DDD ', ' Mike '), insert into table2 ( UID) VALUES (' AAA '), (' AAA '), (' BBB '), (' BBB '), (' BBB '), (' CCC '), (NULL);4. The final desired resultSELECT A.uid, count (b.oid) as Totalfrom table1 as Aleft JOIN table2 as B on a.uid = B.uidwhere A. NAME = ' Mike ' GROUP by a.uidhaving count (b.oid) ！ Start the SQL Resolution tour now!1. fromWhen multiple tables are involved, the output from the left table is used as input to the right table and a v

a.uid, count(b.oid) AS totalFROM table1 AS aLEFT JOIN table2 AS b ON a.uid = b.uidWHERE a. NAME = 'mike'GROUP BY a.uidHAVING count(b.oid) ! Start SQL parsing now! 1. FROM When multiple tables are involved, the output of the left table is used as the input of the right table, and a virtual table VT1 is generated. (1-J1) Cartesian product Calculates the Cartesian product (cross join) of two associated tables to generate a vi

(5) SELECT (5-2) DISTINCT (5-3) TOP ( (1) FROM (1-J) (2) WHERE (3) group by (4) HAVING (6) order by A virtual table is generated for each step, which is used as the input for the next step. These virtual tables are not available to callers. Only the virtual tables generated in the last step are returned to the callers. If no clause is specified in the query, the corresponding steps are skipped. Next we will briefly describe these different logical steps. (1)FROMThe FROM stage identifies the

(5) SELECT (5-2) DISTINCT (5-3) Top ( (1) from (1-j) (2) WHERE (3) GROUP by (4) Having (6) Order by Each step generates a virtual table that will act as the next input. These virtual tables are not available to callers, and only the virtual tables that were generated in the last step are returned to the caller. If you do not specify a clause in the query, the corresponding step is skipped. The next step is to briefly describe these different logical steps. (1) the From from phase ide

table1 (uid,name) VALUES (' AAA ', ' Mike '), (' BBB ', ' Jack '), (' CCC ', ' Mike '), [' DDD ', ' Mike '), insert into table2 ( UID) VALUES (' AAA '), (' AAA '), (' BBB '), (' BBB '), (' BBB '), (' CCC '), (NULL);4. The final desired resultSELECT A.uid, count (b.oid) as Totalfrom table1 as Aleft JOIN table2 as B on a.uid = B.uidwhere A. NAME = ' Mike ' GROUP by a.uidhaving count (b.oid) ！ Start the SQL Resolution tour now!1. fromWhen multiple tables are involved, the output

', ' 2014-4-28 '); Insert into Borrow (cardid,bookid,borrowdate) VALUES (' VVV ', ' ddd ', ' 2014-4-27 '); Insert into Borrow (cardid,bookid,borrowdate) VALUES (' www ', ' aaa ', ' 2014-4-27 '); Insert into Borrow (cardid,bookid,borrowdate) VALUES (' www ', ' CCC ', ' 2014-4-26 '); The table information is as follows: Book------> Reader-------> Borrow 3. Query the number of readers and details of the people who borrow books in Unit a Number: With VT1