Performing a Join Between Tables in Different Databases - MySQL Cookbook, 2nd Edition [Book]
Connect the data in two tables by using their relationships with a third table. View all the records from On the Database Tools tab, in the Show/Hide group, click Relationships. On the Design tab, in the .. See Also. Join tables and queries. Like many traditional database systems, RethinkDB supports JOIN commands to combine data from multiple tables. In RethinkDB joins One to many relations; Many to many relations; Resolving field name conflicts; Read more. Table Join. Joins are the most important thing in relational databases. They are used to join two or more different tables on a point in which both the tables match the same.
An example that uses the Northwind sample database Note: You may want to make a backup copy of the Northwind sample database, and then follow this example by using the backup copy. Suppose you have a new opportunity: They supply every category of food product that you broker.
They are a fairly big business, and want your assurances that you can provide them access to enough potential sales to make it worthwhile: Can you provide them with the market they require?
The data you need to answer this question is found in two places: These tables are linked to each other by an Orders table. Relationships between the tables have already been defined. In the Orders table, each order can have only one customer, related to the Customers table on the CustomerID field. Thus, a given customer can have many orders, each of which has many order details. Build the query in Design view Open the Northwind database.
On the Create tab, in the Queries group, click Query Design. All three tables appear in the query design workspace. In the Customers table, double-click the City field to add it to the query design grid.
This causes only those records where the customer is in one of these two cities to be included in the query.
Guide to table relationships
The fields are added to the query design grid. In the ShippedDate column in the query design grid, select the Field row. Replace [ShippedDate] with Year: This creates a field alias, Year, that allows you to use just the year portion of the value in the ShippedDate field. In the UnitPrice column in the query design grid, select the Field row. Replace [UnitPrice] with Sales: This creates a field alias, Sales, that calculates the sales for each record.
On the Design tab, in the Query Type group, click Crosstab. Two new rows, Total and Crosstab, appear in the query design grid.
Table joins in RethinkDB - RethinkDB
In the City column in the query design grid, click the Crosstab row, and then click Row Heading. This makes city values appear as the row headings that is, the query returns one row for each city.
In the Year column, click the Crosstab row, and then click Column Heading. This makes year values appear as the column headings that is, the query returns one column for each year. In the Sales column, click the Crosstab row, and then click Value. This makes sales values appear at the intersection of rows and column that is, the query returns one sales value for each combination of city and year. In the Sales column, click the Totals row, and then click Sum.
This causes the query to sum the values in this column. You can leave the Totals row for the other two columns at the default value of Group By, because you want to see each value for these columns, not aggregate values.
- Create a query based on multiple tables
- Basic SQL Join Types
- Table joins in RethinkDB
Top of Page View all the records from two similar tables Sometimes, you will want to combine data from two tables that are identical in structure, but one of them is located in another database. Consider the following scenario. Suppose you are an analyst working with student data.
You are embarking on a data sharing initiative between your school and another school, so that both schools can improve their curricula. For some of the questions you want to explore, it would be better to look at all records from both schools together, rather than each school's records separately. You could import the other school's data into new tables in your database, but then any changes to the other school's data would not be reflected in your database.
A better solution would be to link to the other school's tables, and then create queries that combined the data when you run them. You would be able to analyze the data as a single set, rather than performing two analyses and trying to interpret them as if they were one. To view all the records from two tables with identical structure, you use a union query. Union queries cannot be displayed in Design view. Create a union query by using two tables On the Create tab, in the Queries group, click Query Design.
A new query design grid opens, and the Show Table dialog box appears. In the Show Table dialog box, click Close. On the Design tab, in the Query Type group, click Union. The query switches from Design view to SQL view. At this point, the SQL view object tab is empty. Field names should be enclosed in square brackets, and separated by commas. The cursor moves down one line in SQL view. Type FROM, followed by the name of the first of the tables you want in the query.
You should include the same fields from this table that you included from the first table, and in the same order. Type FROM, followed by the name of the second table you want to include in the query. Type a semicolon ; to indicate the end of your query. Your results appear in Datasheet view. Designate a primary data source Drag at least one field from your primary data source into the view to designate it as the primary data source. In the Data pane, click the data source that you want to designate as the primary data source.
In this example, Sample - Superstore is selected. Drag the fields you want to use from the data source into the view. In this example, a view is created that shows Sales by Segment and Category.
SQL JOIN | How to link Relational Databases - 1&1 IONOS
Designate a secondary data source Any fields used in the view from data sources that are not the primary data source or active links automatically designate subsequent data sources as the secondary data source. In the Data pane, click the data source that you want to designate as the secondary data source.
In this example, the Sales Plan data source is selected. When you complete this step, an orange bar displays down the left side of the Data pane.Joining two tables two different databases
The orange bar indicates the secondary data source. In addition to the orange bar, broken link icons display next to potential linking fields. Click a broken link icon to establish a relationship between the secondary and primary data sources.
This is the field that determines the level of detail that Tableau should aggregate to. In this example, Segment is the linking field.
Blend Your Data
If a broken link icon does not appear next to the field that should be the linking field or no broken links appear, see Step 4: Optional Define or edit relationships. Drag the fields you want to use from the secondary data source into the view. In this example, Sales Plan field is used on the Detail card to change the level of detail of the view.
Optional Define or edit relationships Tableau detects when a field from the primary data source also exists in a secondary data source, and indicates that the fields are potential linking fields by marking them with a broken link icon in the Data pane.
You click a broken link icon to establish a relationship between the primary and secondary data sources, and have Tableau blend data from both data sources on a single sheet. You must have at least one linked field in order to use data from the secondary data source.
In the Relationships dialog box, verify that the primary data source is selected from the Primary data source drop-down list. In this example, the Sample - Superstore data source is selected. Select the secondary data source in the Secondary data source pane, select Custom in the relationships list, and then click the Add button.