Daily learning 2

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1.SQL Sentence Niuke brush questions

2. Force button brush questions

3.JavaWeb Study

4. Reading a book

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1.SQL Sentence Niuke brush questions

It's painted 5 individual  

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This question is a comprehensive investigation ,

Examination site 1：  The weight removal of the first line distinct Use , user id Need to be heavy , But the number of questions does not need to be repeated , because A Made a title 1, and B Made a title 1 It can't be counted as just doing one topic .

Examination site 2： Fuzzy query in the third line %, Review the ,  stay SQL Two wildcards can be used in the statement ： Underline （_） And percent （%）, The underscore can represent any character , The percent sign can represent any number of characters , Include 0 Characters .

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This question is also a comprehensive investigation

Even the table query Remember format select xxx from xxx1 left join xxx2 on（）...  When there are the same keywords in two tables , Use table names to distinguish , As in the question device_id, It refers to device_id, To write " surface 1 name .device_id", It means to represent two congruences . We must distinguish , Otherwise, the code will be ambiguous , Causes compilation errors . If the table name is too long , You can also alias the table name . Finally, don't forget to follow question_id  Sort , Because the title is required to be in ascending order ,asc It can be omitted .

2. Force button brush questions

The third question has made new progress

Finally, the one-way linked list is changed into a two-way linked list , At last .

3.JavaWeb Study

I finished learning as planned CSS part . Made several notes .

4. Reading a book

see 《MySQL Must learn knowledge 》 Read six chapters