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I come to know that this is used to speed up data retrieval..I like to know more about it .Thanks .
Indexing is a way of sorting a number of records on multiple fields. Creating an index on a field in a table creates another data structure which holds the field value, and pointer to the record it relates to. This index structure is then sorted, allowing Binary Searches to be performed on it.
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I want to clean this data. There are text strings for dates and user_ids. Every date from the rows is assigned for every id. How do we do this using SQL?
enter image description here schedules table
I don't know yet. I am expecting every date from the rows is assigned for every id.
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is any scientific reason to create a table with self join and 1 to many relation in the same table >>>
what i need is explain why we can't do this
thanks for your time .
Yes, they are perfectly valid situations that need such relations.
For example when you store a Tree on a table. Each node will have links to its childs (through a ParentId column), so it will have a relation 1 to many with itself.
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I have to optimize a bunch of many table and data included SQL queries, and I would like to ask some questions:
1) There are situations, when the same functions are needed in different queries. Which results lower processor time: if the functions are calculated separately in every queries or if it is calculated in one query, and they are linked through each other?
2) When creating queries, which is better in giving table relationships? If I have 1 main query, and all of the other queries are related to that, or if there is a serial connection between all the tables?
The 2 main tables are relatively big (~30MB) Excel-tables.
Thank you in advance.
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I'm using SQL Server DB and I would like to write query which will look for a fields with two or more slashes in it, lets say we have these rows:
1. abc/def/g
2. abcd/efg
3. a/b/c/d/e/f/g
So it should return 1st and 3rd row! What is the easiest way to do so?
Thanks in advance!
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this is more of a general question I came across today.
To update an sql record I noticed that it is common practice where I work to store the old record values, remove the record, and then add a new record with the old values plus one or more values that have been changed.
Wouldn't it be easier to simply update only the values you want to edit? Or, is there some reason for the entire removal that I'm not seeing?
Thank you.
If you want to update a record, then just update it using update query. It's not a good practice to remove the entire row and inserting back after applying modification instead of an update query.