## Exercise #11 (tips and solutions) |
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Existence of standard aggregate function AVG solves all issues: However the forum shows the attempts to be distant from the general "grey" mass. Here is quite equivalent solution which, the truth, adds the extra operation in the procedural plan: Correctness of the following decision depends on available restrictions: Namely, if SUM (speed) ignores rows with NULL value of speed, expression SUM(1) will count up total of rows in PC table, which, in essence, is equivalent to use of COUNT(*). As a result the sum of speeds of all the personal computers except for rows with unknown speed will be calculated in numerator which will be divided by the total number of rows. Therefore all the presented solutions will be equivalent, if NULL values are inadmissible, i.e. there is restriction NOT NULL on a speed column . To return to discussion of exercise #11 To solve a problem on SQL-EX.RU |

- CHOOSE function
- Data type conversion and CAST function page 2
- COUNT DISTINCT and window functions
- Explicit join operations
- Exercise #28
- Exercise #8 (tips and solutions) page 2
- Exercise #8 (tips and solutions)
- Exercise #7 (tips and solutions)
- Exercise #6 (tips and solutions)
- Exercise #2 (tips and solutions)

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AND
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exercise 19
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exercise 32
exercise 37
exercise 39
exercise 46
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exercise 55
exercise 56
exercise 57
exercise 7
exercise 70
exercise 8
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