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v4.0
    v4.0

    coalesce() | Coalesce (V4.1)

     V4.1 

    Parameters, Value

    Coalesce function merges multiple (≥2) columns into one column, it keeps the first non-null value in each row and disgards the rest of the values. If any row contains only null values and there is no <constant> parameters, then that row results in null ultimately.

    if columns are not homologous: when used in WITH, table() will first make a Cartesian Product Combination of all columns and its homologous columns before merging; when used in RETURN, table() will trim all columns and their homologous columns before merging.

    Syntax:

    • Format: coalesce(<column1>, <column2>, ..., <constant>)
    • Parameters: see table below
    • Value: ATTR
    Name Category Specification Description
    <column> ATTR / The column to be merged
    <constant> ATTR Not mandatory Non- null constant; if all values of a column of data are null,then merge the data from that column and take the value of the constant

    Alias (Homologous)

    Example: find 10 cards, return the time of opening cards; return the expiry time if the opening time is null

    find().nodes({@card}) as n
    limit 10
    return coalesce(n.open_date, n.expire_date) 
    

    Example: find 10 cards, return the time of opening cards; return the expiry time if the opening time is null; return 0 when the expiry time is null

    find().nodes({@card}) as n
    limit 10
    return coalesce(n.open_date, n.expire_date, 0) 
    

    WITH Alias (Non-homologous)

    Example:

    uncollect [1,2,3] as a1
    uncollect [4,5] as a2
    with coalesce(a1, a2) as a3
    return a3
    

    RETURN Alias (Non-homologous)

    Example:

    uncollect [1,2,3] as a1
    uncollect [4,5] as a2
    return coalesce(a1, a2)
    
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