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script to generate type cast chart
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‎documentation/reference/sql/cast.md‎

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## Casting table
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The below chart illustrates the explicit and implicit cast available in QuestDB:
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<!-- the image can be regenerated via the script at scripts/generate_type_cast_chart.py -->
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![Table showing the different possibilities the cast function supports, those are defined by an input and output types](/images/docs/castmap.jpg)
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| From \ To | String | Boolean | Char | Byte | Short | Int | Long | Long256 | Float | Double | Decimal | Date | Timestamp | Symbol | Binary |
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| --------- | ------ | ------- | ----- | ----- | ----- | ----- | ----- | ------- | ----- | ------ | ------- | ----- | --------- | ------ | ------ |
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| String | | `E` | `E*` | `E` | `E` | `I` | `I` | `I` | `I` | `I` | `E` | `I` | `I` | `I` | `N/A` |
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| Boolean | `I` | | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` | `I` | `I` | `I` | `N/A` |
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| Char | `I` | `N/A` | | `E*` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` | `I` | `I` | `I` | `N/A` |
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| Byte | `I` | `E*` | `I` | | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` |
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| Short | `I` | `E*` | `E*` | `I` | | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` |
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| Int | `E` | `E*` | `E*` | `E*` | `E*` | | `I` | `I` | `I*` | `I` | `I` | `I` | `I` | `I` | `N/A` |
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| Long | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | | `I` | `E*` | `I*` | `I` | `I` | `I` | `E` | `N/A` |
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| Long256 | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | `E*` | | `E*` | `E*` | `N/A` | `E*` | `E*` | `E*` | `N/A` |
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| Float | `E` | `N/A` | `E*` | `E*` | `E*` | `I*` | `I*` | `I*` | | `I` | `E*` | `I*` | `I*` | `I` | `N/A` |
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| Double | `E` | `N/A` | `E*` | `E*` | `E*` | `E*` | `I*` | `I*` | `E*` | | `E*` | `I*` | `I*` | `E` | `N/A` |
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| Decimal | `E` | `N/A` | `N/A` | `E!` | `E!` | `E!` | `E!` | `N/A` | `E*` | `E*` | | `N/A` | `N/A` | `N/A` | `N/A` |
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| Date | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | `I` | `I` | `E*` | `I*` | `N/A` | | `I` | `E` | `N/A` |
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| Timestamp | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | `I` | `I` | `E*` | `I*` | `N/A` | `I*` | | `E` | `N/A` |
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| Symbol | `I` | `E` | `E` | `E` | `E` | `E` | `I` | `I` | `E` | `I` | `N/A` | `I` | `I` | | `N/A` |
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| Binary | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` |
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#### Legend
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- `E`: Explicit cast (using the `cast` function or `::` operator)
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- `I`: Implicit cast
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- `*`: The cast operation might lead to precision loss
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- `!`: The cast operation throws an error when if it would lead to precision
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loss
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```questdb-sql title="Queries"
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SELECT

‎scripts/generate_type_cast_chart.py‎

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import matplotlib.pyplot as plt
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import matplotlib.patches as mpatches
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markdown_table = """
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| From \\ To | String | Boolean | Char | Byte | Short | Int | Long | Long256 | Float | Double | Decimal | Date | Timestamp | Symbol | Binary |
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| --------- | ------ | ------- | ----- | ----- | ----- | ----- | ----- | ------- | ----- | ------ | ------- | ----- | --------- | ------ | ------ |
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| String | | `E` | `E*` | `E` | `E` | `I` | `I` | `I` | `I` | `I` | `E` | `I` | `I` | `I` | `N/A` |
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| Boolean | `I` | | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` | `I` | `I` | `I` | `N/A` |
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| Char | `I` | `N/A` | | `E*` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` | `I` | `I` | `I` | `N/A` |
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| Byte | `I` | `E*` | `I` | | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` |
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| Short | `I` | `E*` | `E*` | `I` | | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `I` | `N/A` |
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| Int | `E` | `E*` | `E*` | `E*` | `E*` | | `I` | `I` | `I*` | `I` | `I` | `I` | `I` | `I` | `N/A` |
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| Long | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | | `I` | `E*` | `I*` | `I` | `I` | `I` | `E` | `N/A` |
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| Long256 | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | `E*` | | `E*` | `E*` | `N/A` | `E*` | `E*` | `E*` | `N/A` |
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| Float | `E` | `N/A` | `E*` | `E*` | `E*` | `I*` | `I*` | `I*` | | `I` | `E*` | `I*` | `I*` | `I` | `N/A` |
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| Double | `E` | `N/A` | `E*` | `E*` | `E*` | `E*` | `I*` | `I*` | `E*` | | `E*` | `I*` | `I*` | `E` | `N/A` |
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| Decimal | `E` | `N/A` | `N/A` | `E!` | `E!` | `E!` | `E!` | `N/A` | `E*` | `E*` | | `N/A` | `N/A` | `N/A` | `N/A` |
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| Date | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | `I` | `I` | `E*` | `I*` | `N/A` | | `I` | `E` | `N/A` |
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| Timestamp | `E` | `E*` | `E*` | `E*` | `E*` | `E*` | `I` | `I` | `E*` | `I*` | `N/A` | `I*` | | `E` | `N/A` |
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| Symbol | `I` | `E` | `E` | `E` | `E` | `E` | `I` | `I` | `E` | `I` | `N/A` | `I` | `I` | | `N/A` |
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| Binary | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` | `N/A` |
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"""
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# --- Parse Markdown into matrix ---
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lines = [line.strip() for line in markdown_table.strip().split("\n") if line.strip()]
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header = [h.strip() for h in lines[0].split("|")[1:-1]] # remove leading/trailing pipe
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rows = []
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matrix = {}
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for line in lines[2:]: # skip header + separator
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parts = [p.strip().strip("`") for p in line.split("|")[1:-1]]
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row_name, values = parts[0], parts[1:]
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matrix[row_name] = dict(zip(header[1:], values)) # map To-cols to values
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rows.append(row_name)
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cols = header[1:]
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# --- Color mapping ---
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color_map = {
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"": "white",
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"I": "#a6d96a", # implicit
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"E": "#fdae61", # explicit
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"I*": "#313695", # implicit precision loss
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"E*": "#d73027", # explicit precision loss
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"E!": "#e08214", # explicit warning
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"N/A": "#7f7f7f" # grey
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}
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# --- Plot ---
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fig, ax = plt.subplots(figsize=(5, 4))
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for i, row in enumerate(rows):
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for j, col in enumerate(cols):
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val = matrix[row].get(col, "")
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ax.add_patch(plt.Rectangle(
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(j, i), 1, 1,
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facecolor=color_map.get(val, "white"),
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edgecolor="black", linewidth=0.5
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))
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# Configure ticks
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ax.set_xticks([i + 0.5 for i in range(len(cols))])
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ax.set_yticks([i + 0.5 for i in range(len(rows))])
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ax.set_xticklabels(cols, rotation=90)
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ax.set_yticklabels(rows)
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# Put X axis labels at the top
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ax.xaxis.tick_top()
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ax.set_xlim(0, len(cols))
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ax.set_ylim(0, len(rows))
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ax.invert_yaxis()
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ax.set_aspect("equal")
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# Axis labels
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ax.set_xlabel("TO", labelpad=20)
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ax.xaxis.set_label_position("top")
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ax.set_ylabel("FROM", labelpad=20)
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ax.yaxis.set_label_position("left")
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# Legend centered at bottom
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legend_elements = [
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mpatches.Patch(facecolor="#a6d96a", edgecolor="black", label="Implicit"),
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mpatches.Patch(facecolor="#fdae61", edgecolor="black", label="Explicit"),
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mpatches.Patch(facecolor="#313695", edgecolor="black", label="Implicit (precision loss)"),
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mpatches.Patch(facecolor="#d73027", edgecolor="black", label="Explicit (precision loss)"),
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mpatches.Patch(facecolor="#7f7f7f", edgecolor="black", label="N/A")
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]
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ax.legend(handles=legend_elements,
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bbox_to_anchor=(0.5, -0.05), loc="upper center", ncol=3, frameon=False)
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# Save directly to file
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path = "../static/images/docs/castmap.jpg"
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plt.savefig(path, dpi=300, bbox_inches="tight")
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plt.close()
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print("file written to: " + path)

‎static/images/docs/castmap.jpg‎

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