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Find intersection of two nested lists?
...but because set membership is in average O(1) (for example when using hash table), it is big difference,for example because amortized time is guaranteed.
– miroB
Dec 4 '17 at 20:27
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MySQL DISTINCT on a GROUP_CONCAT()
I am doing SELECT GROUP_CONCAT(categories SEPARATOR ' ') FROM table . Sample data below:
6 Answers
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Mysql order by specific ID values
...and FIELD function.
See http://lists.mysql.com/mysql/209784
SELECT * FROM table ORDER BY FIELD(ID,1,5,4,3)
It uses Field() function, Which "Returns the index (position) of str in the str1, str2, str3, ... list. Returns 0 if str is not found" according to the documentation. So actually you sort th...
Cartesian product of multiple arrays in JavaScript
...in the browsers, see:
http://caniuse.com/
https://kangax.github.io/compat-table/
To see the support in Node versions, see:
http://node.green/
To use modern syntax on platforms that don't support it natively, use Babel or TypeScript:
https://babeljs.io/
https://www.typescriptlang.org/
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Equivalent of LIMIT and OFFSET for SQL Server?
... ROW_NUMBER() OVER (ORDER BY SortCol1, SortCol2, ...) AS RowNum
FROM Table
WHERE <whatever>
)
SELECT *
FROM Results_CTE
WHERE RowNum >= @Offset
AND RowNum < @Offset + @Limit
The advantage here is the parameterization of the offset and limit in case you decide to change your p...
Sqlite: CURRENT_TIMESTAMP is in GMT, not the timezone of the machine
I have a sqlite (v3) table with this column definition:
11 Answers
11
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When is SQLiteOpenHelper onCreate() / onUpgrade() run?
I have created my tables in my SQLiteOpenHelper onCreate() but receive
15 Answers
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Alternate output format for psql
I am using PostgreSQL 8.4 on Ubuntu. I have a table with columns c1 through cN . The columns are wide enough that selecting all columns causes a row of query results to wrap multiple times. Consequently, the output is hard to read.
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Creation timestamp and last update timestamp with Hibernate and MySQL
...ons, you can use @PrePersist and @PreUpdate event hooks do this:
@Entity
@Table(name = "entities")
public class Entity {
...
private Date created;
private Date updated;
@PrePersist
protected void onCreate() {
created = new Date();
}
@PreUpdate
protected void onUpdate() {
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Join vs. sub-query
...and query-specific.
Historically, explicit joins usually win, hence the established wisdom that joins are better, but optimisers are getting better all the time, and so I prefer to write queries first in a logically coherent way, and then restructure if performance constraints warrant this.
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