DatabaseLink`
DatabaseLink`

SQLSelect

SQLSelect[conn,table]

extracts data from a table in an SQL connection.

SQLSelect[conn,table,cols]

extracts data from particular columns.

SQLSelect[conn,table,cols,cond]

only extracts data that matches cond.

Details

  • To use SQLSelect, you first need to load DatabaseLink using Needs["DatabaseLink`"].
  • The following options can be given:
  • "Distinct"Falsewhether to return only distinct results
    "FetchSize"AutomaticJDBC driver hint for filling result sets
    "GetAsStrings"Falsewhether to return the results as strings
    "MaxFieldSize"Automaticbyte limit for variable-length column types
    "MaxRows"Automaticthe maximum number of rows to return
    "ShowColumnHeadings"Falsewhether to return headings with the results
    "SortingColumns"Nonehow to sort the data
    "ColumnSymbols"Nonesymbols to be associated with results
    "Timeout"$SQLTimeoutthe timeout for the query

Examples

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Basic Examples  (1)

If you find that the examples in this section do not work as shown, you may need to install or restore the example database with the DatabaseLink`DatabaseExamples` package, as described in Using the Example Databases.

Open a connection:

Select all data from a table:

Select only certain columns:

Join data from multiple tables:

Select data matching a condition:

Select data matching a pattern:

Select data matching a list:

Scope  (1)

Select data matching a condition:

Combine conditions using And and Or:

Options  (8)

"Distinct"  (1)

Retrieve unique values:

"FetchSize"  (1)

The "FetchSize" option suggests to the JDBC driver a number of rows to fetch on each visit to the database. Increasing this parameter reduces the amount of network traffic required to execute a query, at the cost of memory used:

Compute memory in use, including both kernel and Java layers:

Fetch a large result with a small fetch size:

Reset:

Fetch a large result with a large fetch size:

"GetAsStrings"  (1)

Retrieve data without converting it to Wolfram Language types:

"MaxFieldSize"  (1)

For some variable-length column types the "MaxFieldSize" option can be used to limit the number of bytes returned for a field:

Create a table with a VARCHAR field:

Insert string data:

Select string contents, limiting byte length of results:

"MaxRows"  (1)

Limit the number of rows returned in a result:

"ShowColumnHeadings"  (1)

Include column names as the first row of the results:

"SortingColumns"  (1)

Specify columns to order by:

"ColumnSymbols"  (1)

Supply a list of symbols for query results to be assigned to:

Create symbols automatically:

Supply a function to operate on column names and results. If column headings have not been requested, the first argument to the function will be Null:

Applications  (1)