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--- transformations:merge [2017/05/01 22:53] – dmitry
+++ transformations:merge [2021/04/05 00:33] – craigt
@@ Line 1: / Line 1: @@
-===== Merge another table =====
+{{ transformations:MergeAction.png}}
+====== MERGE ANOTHER TABLE ======
+Category: Transform / Basic\\
-This transformation appends one or more columns from another table where certain columns in both tables match.
+\\
+=====Description=====
+This action appends one or more columns from another table where the values in certain columns in both tables match.
-There are three possible merge modes:
+There are three possible merge modes:\\
+====Lookup Mode====
+Retrieve the //first// matching combination from the other table. Any subsequent combinations are ignored.\\
+\\
+====Left Join Mode====
+Retrieve //all// matching combinations from the other table. This mode can increase the number of rows in the current table as rows are duplicated to hold any multiple matches from the second dataset.\\
+\\
+====Full Join Mode====
+Include all combinations of keys from both tables. Equivalent to the full outer join in SQL.  This mode could potentially return very large datasets.\\
-  * Lookup Mode -- get **first** matching combination from the other table. If there are other combinations they are ignored.
+\\
-  * Left Join Mode -- get **all** matching combinations from the other table. It can increase number or rows in the current table.
+=====Limitations=====
-  * Full Join Mode -- include all combinations of keys from both tables. Equivalent to the full outer join in SQL.
+The resulting table after Merge can't have more than 134,217,728 rows.\\
-EXAMPLE
+\\
+=====Use cases=====
+  * (Lookup Mode) Look up replacement values for common misspellings or abbreviations.
+  * (Left Join Mode) Blend in additional data from other tables into the primary dataset.
+  * (Full Join Mode) Combine two entire datasets to be cleaned and consolidated downstream.
-**Table 1:** The longest rivers in the world
+\\
+=====Action settings=====
+^Setting^Description^
+|Add columns from table|Select table that will return columns to the current dataset where values match.|
+|Where all these columns match|Select the columns within the current dataset (left drop-down) and the second dataset (right drop-down) where\\ values will match.  To define multi-columnar matches, use the //Add more matching columns// to select additional matching columns in each dataset.|
+|Merge mode|Options:\\  //Lookup// (for each row in this table, get any one matching row from the second table and ignore other matches),\\ //Left join// (for each row in this table add all matching rows from the second table),\\ //Full join// (add matching and non-matching rows from both tables).|
+|Return columns|From the list, select the columns from the second dataset that will be appended to the current dataset.|
+The reference to the second table will appear as a dotted line connecting this action to the second dataset in the application window.
-^  River  ^  Length (km)  ^  Continent  ^
+\\
-| Nile  |  6650  |  Africa  |
+=====Examples=====
-| Amazon  |  6400  |  South America  |
-| Yangtze  |  6300  |  Asia  |
-| Mississippi  |  6275  |  North America  |
-**Table 2:** The outflow
-^  River  ^  Outflow  ^
+**Objective:** Merge the "Outflow" column of Table 2 into Table 1 based on matching values in the "Rivers" columns in both tables.\\
-| Nile  |  Mediterranean  |
-| Amazon  |  Atlantic Ocean  |
-| Yangtze  |  East China Sea  |
-| Mississippi  |  Gulf of Mexico  |
+**Table 1:** The longest rivers in the world\\
-**Objective:** Merge the "Outflow" column of Table 2 into Table 1
+^River  ^Length (km)  ^Continent  ^
+| Nile  |  6650|Africa  |
+| Amazon  |  6400|South America  |
+| Yangtze  |  6300|Asia  |
+| Mississippi  |  6275|North America  |
+\\
+**Table 2:** The outflow\\
-**Transformation:**
+^River  ^Outflow  ^
+| Nile  |Mediterranean  |
+| Amazon  |Atlantic Ocean  |
+| Yangtze  |East China Sea  |
+| Mississippi  |Gulf of Mexico  |
+\\
+**Action parameters:**
-  * Add columns from table: Table 2
+> Add columns from table: Table 2
-  * Column: Outflow
+> Where values in the Table 1 "River" column match values in the Table 2 "River" column
-  * Merge mode: Add more rows to this table and all matching rows from Table 2 (i.e. do left join)
+> Merge mode: Left join (add all matching rows from Table 2 to Table 1)
+> Return column: Outflow
-**Result:**
+\\
+**Result:**\\
-^  River  ^  Length (km)  ^  Continent  ^  Outflow  ^
+^River  ^Length (km)  ^Continent  ^Outflow  ^
-| Nile  |  6650  |  Africa  |  Mediterranean  |
+| Nile  |  6650|Africa  |Mediterranean  |
-| Amazon  |  6400  |  South America  |  Atlantic Ocean  |
+| Amazon  |  6400|South America  |Atlantic Ocean  |
-| Yangtze  |  6300  |  Asia  |  East China Sea  |
+| Yangtze  |  6300|Asia  |East China Sea  |
-| Mississippi  |  6275  |  North America  |  Gulf of Mexico  |
+| Mississippi  |  6275|North America  |Gulf of Mexico  |
-=== See also ===
+\\
+=====See also=====
   * [[transformations:append|Append another table]]
+  * [[transformations:lookup|Lookup]]