To create a join calculation, click the join icon between the tables that have a broken join, click the field whose format needs to be modified, and then select Create Join Calculation. A join calculation supports a subset of calculations that lets you modify the format of the join key in one or more tables that you want to combine. You can change the format of a field (including its data type) in the join dialog to make the join keys match by creating a join calculation. To fix a broken join, use one of the following suggestions: If the data types of the join keys don't match, the join breaks, which is indicated by a red exclamation point and the error text "type mismatch between join fields". For more information about how to connect to a custom SQL query from Tableau, see Connect to a Custom SQL Query.īroken table joins and cross-database joinsīefore you join tables (from the same data source or using a cross-database join), make sure that the data types of the join keys match. This option requires some knowledge about writing SQL queries and assistance from a database expert if possible. You can pre-aggregate the tables before joining them with a GROUP BY clause. Use custom SQL: Tableau supports using custom SQL for connecting to multiple tables in a data source. For more information, see Removing Duplicate Data with LOD Calculations (Link opens in a new window) in the Tableau Knowledge Base. You could also use a Level of Detail Expression to delete the duplicate data. In this case, in the view replace Salary with a calculated field that uses the following formula: SUM ()/ COUNT (). For more information, see Relate Your Data.Ĭhange the aggregation: Depending on your analysis, you can use the MIN or AVG aggregation to remove over-counting.įor example, if you change the aggregation of Salary from SUM to MIN or from SUM to AVG.Ĭreate a calculated field that removes the duplicate values: You can create a calculation that divides the sum of the field being duplicated by the number of instances of the field that is causing the duplication.įor example, the Salary values are being duplicated by the number of instances of Employee ID for Wilson, Henry. Relate the data: Instead of creating a join, which might duplicate your data, you can use relationships. To help resolve this issue, you can do one of the following: For more information on cardinality between tables, see Optimize Relationship Queries Using Performance Options. This is an example of one-to-many cardinality (one employee ID in Table 1 has multiple results in Table 2). If you join these tables on Employee ID, an employee's salary is counted more than once because the employee is associated with multiple departments. The second table contains organizational information, such as department names. This can cause values to be over-counted.įor example, suppose you have two tables. The first table contains employee information, such as employee ID and salary. When multiple tables are treated as one table, after the tables are joined, all tables are queried. In some cases, Tableau treats the multiple tables as one table. When you connect to and join multiple tables together, you set up a denormalized version of the data. For information about how Tableau handles combining data from different levels of detail (such as many-to-many relationships), see Cardinality and Referential Integrity. For more information about relationships, see Relate Your Data. The symptom described in this article is about a specific defect which is already fixed in the latest version of Tableau Prep Builder.ĬauseThis is related to a known issue which has been addressed in a more recent version of the product.Note: If your join is mis-counting data, it could be a sign you should be using a relationships instead. Note: To maintain performance, even if you select this setting, a data sample limit of 1 million rows is applied to Aggregate and Union step types and a data sample limit of 3 million rows is applied to Join and Pivot step types. ResolutionUpgrade Tableau Prep Builder to 2020.2.1 or later. The output will still utilize all the data, but the preview window will show "Sampled" where all data should be available in the preview.ĮnvironmentTableau Prep Builder 2019.4.2, 2020.1.1.Previewing cleaned steps shows the data as being sampled and limit to 275K rows, regardless if "Use All Data" is selected.In other words, you may notice the following scenarios: When selecting the "Use all Data" option for a data source in Tableau Prep, the data is showed as sampled in the flow regardless.
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